Well, there's "accuracy" and "playability".
Many folks criticize the TNE system on playability. I can't speak to T4.
T4 is between TNE and MT in terms of playability; it kept the crunchy design system that needed people to cross check each other to get legal ship/vehicle/weapon designs from TNE, but the character scale side is much closer to CT, and it's got the nD6 <= Stat+Skill that is carried on into T5.
I've seen two camps of T4 users dominant over the years: those who ignore FF&S2, use the far less optimized QSDS or port ships from CT/MT/T20, and the ones who embrace the complexity, often adding in options galore from expansions and using the "definitive sensor rules"... there's a spectrum between those two, but it lends itself as a ruleset to those positions. Camp 3 is "Used it, didn't like it, went back/on to another edition"
This may be selection bias in action. The core, by itself, is a very playable edition. It's only when you start adding the splats that it becomes overtaken with complexity.
Also note: QSDS (Quick Ship Design System) is built from FF&S1 (as FF&S2 was in development), and has numerous errors as included; it works just fine if you don't want FF&S1 or FF&S2 true compatibility. QSDS2 is QSDS but FF&S2 compliant.
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
SSDS (Simple Ship Design System) is more complex than QSDS, but isn't full up FF&S2; it's comparable to the Brilliant Lances Technical Book (which is a subset/preview of FF&S1...)
I don't know why I like dice by difficulty vs Att for fantasy & supers, but dislike it for Sci-Fi and Space Opera... but I'll note also that the numbers in T4/T5 are particularly bad for my opinions of Att value vs skill value. And T4 was the point I really realized it.