The NTM is a 'work in progress' still, currently applied to:
Ford GT
Honda HPD-<something>
Skip Barber
Nascar Truck, 'new' NW and COT,
The Ovals are fairly good, lack of tyre falloff but the feel is drastically improved imo
The road cars again, imo, have an improved feel but there are more issues, more so the Ford GT and Honda HPD tbh, but I still think it's an improvement and personally really enjoy driving the HPD, even if I'm not talented enough to be properly quick in it
The Skip Barber has changed a fair bit with the NTM, I've only done one practice and then a club england race (at Okayama full) and it was good imo, different to the old model but in a good way and over the course of the race the tyres changed due to wear nicely, I'd say this is the best example of the NTM.
As for the Ford GT specifically, not really spent any proper time with it (I far prefer the HPD), but it's understeery with the default setups, and the 1 or 2 other early setups I tried, I did find initially around Suzuka that once you got into driving it it was ok (eg slowed enough to negate the understeer, rather than ploughing in too quickly and wanting it to oversteer), the rear end would twitch out occasionally but I didn't find it too unmanageable, generally ok but not as nice as the HPD
Oh, and the closing speeds are silly, I much prefer being in the quicker car (eg HPD) than being the one with a quicker car flying past when you least expect it