I owned a 2007 Fg2 for about 6 years.
I really liked the car, though my particular model started having transmission and clutch issues that drove me nuts and Honda gave me the same run around that they'd been giving 6 speed owners for years and years. I got rid of it, and based on the incredibly negative experience I and many many others had just trying to get this simple problem fixed has stained Honda's reputation for me. Heck, I knew people who drove hundreds of miles and stayed up in hotels or at friends just to get a shot at having their transmission serviced by a reasonable dealer.
Anyway that rant aside, there is a lot of likeness between these cars.
The FG2 had a respectable trunk space and carrying capacity for a coupe, but then again it was a pretty big coupe. The Fist manages similar storage space (albeit shaped differently) despite being a significantly smaller car. Plus hatch functionality. Rear seat room is comparable.
Seats, the base seats are nothing to write home about. The Si seats versus Recaros... To me they're both good but flawed. The Recaros are much more heavily bolstered and hold very well and give great support, however they're hard as a rock. The Si's are softer with little support. In the Si my back and especially lower abdomen started to ache and I couldn't find a comfortable posture after several hours and frequently had to arch my back to relieve it and my abdominal area. With the FiST my whole body stays comfortable, but without getting into uneccesarry detail, my midline including tailbone forward get numb and sore. I am currently working on a solution for long drives. More info to come...
Interior build quality is somewhat similar. The plastics in the FiST are considerably more resistant to scuffing and marring. The armrest setup is markedly inferior on the Fist. I'm historically opposed to auto climate, but the way the Fist's works I have somewhat begrudgingly decided I like it. It can fake manual mode passably well. The wipers don't do that cool swipe when you lift the brake pedal from a stop like the Honda.
Low beams in the FiST are noticeably better. The FG's low beams sucked. I miss my Civic's massive 'still legible even though you're looking in a completely different direction and focused on something a mile away' digital speedo something awful. Stereo in the fist may be a hair better overall but you'll miss your factory trunk sub.
Handling is somewhat comparable, though the Fiesta is more lively/nervous feeling, as well as a bit more top heavy. The fist is slightly more prone to oversteer.
I haven't had much experience testing the mettle of the Fist's driver's aids, but they seem pretty competent and well tuned thus far, very much unlike the 8th gen civic's which was a cluster that I felt was more likely to get you into trouble than not.
Steering feel, feedback, weight is quite similar, though the Fist is quite a bit faster ratio from what I recall.
The transmissions are very similar in use! The position of the lever, the length of the throws, the notchiness and general feel, all pretty comparable, though perhaps the fist is a tad less refined if you have a good example of the honda's box. Even the clutch had a similar weight and feedback from what I remember, though the fist's grabs with a tad more authority. The biggest difference between them is the Fist doesn't seem to mind being hurried. An aggressive 1-2 on the Fist seems to be taken in stride. My civic started faltering very early in its life, even on slow shifts. Now granted I have had the Cobb RMM installed from early on, but by the same token, even rock hard triple motor restrictors from boomba on the civic didn't help shifting.
Where the cars tend to vary most is how they make and use power, and especially how the chassis responds powering out of a corner.
The K20 sung and pulled with satisfaction once you got it up high. Down low, as you know, you got nothing. Still, especially with an SRI that car sounded fantastic and was a joy to wring out to redline all the time. It felt like a proper high strung sporty engine should, slightly overdone vtec changeover not withstanding.
The good news is, stock at least, the Fist is a lot of fun to wring out to redline. It doesn't sound as good as a K20 but it is still invigorating. The big difference of course is even down low, if you leave the pedal down for a brief moment, the car starts pulling with a little wave of torque that makes most people furrow their brow in impressed admonishment. It continues pulling pretty well to redline, stock at least. Also, while the car's induction note isn't quite up to par, with the windows down the turbo makes pretty delightful noises, buy an intake if you want to hear them clearly all the time.
You may be wondering why I emphasized the engine's personality stock. Well, if you pursue the normal Cobb style tuning path, it extracts more power from down low and midrange, leaving the top end relatively unchanged. So while it will feel like a monster up to 4-5ish grand, it is going to feel like the engine is running out of steam up high by comparison. If you have driven wrx's they are probably going to be representative. If you absolutely have to have the run it to redline with a constantly ascending power band feel, I'd say either enjoy the stock power, or expect a turbo upgrade in the future.
So this brings me to my last point, and it is a lengthy one, but worth noting for someone coming out of a well sorted FF into another well sorted FF and expecting much of the same...
The civic has low torque and a mechanical LSD. The Fist has high torque and an electronic brake based "dif." They are VERY DIFFERENT in practice.
The Si makes use of it's power well and steers fairly neutrally out of a corner as a result. The Fist on the other hand feels less natural as it brakes selectively both to put power down but also minimize under steer.
As a result it feel like it is dramatically grabbing the nose and pulling it toward the direction of travel with an unnatural fervor. You can feel it through the chassis and you can definitely feel it in the wheel as it pulls this way and that as a result of natural torque steer and the car's computers fighting it to varying degrees of success.
Yes, purists be damned, it is a bit involved on the "computery" side of things and some folks may take issue (especially when you cannot disable it at all), but...
It is very capable and it is fun to have a fwd so angrily ignore the ass end and just shoot for wherever the front is trying to go. Yeah, we're in the era of brake based power distribution. It ain't perfect and it is a faaar cry from the neutral steering of an FR that purists diefy, but damn it sure is something!
So yeah, just be aware the first time you hammer it out of a bend.
If you have other questions or want any insight I might be able to provide feel free to ask. The FG2 is a fantastic car, and if I hadn't had all those transmission problems there's a chance I'd still have it today. Still, the FiST is handily my favorite over the Si and my old FR-S.