I just installed the RWD version my Long Range RWD and they're great.
@huyzee How low are you? I heard some minor binding near the Tein recommended settings but nothing yet at max ride height.
I have a 2018 model and the suspension was overly stiff, even after 130k miles. The rear seemed about right but the front would beat itself up on sharp bumps. Its likely this car was built with AWD front springs being its a limited edition. Stock, the car sat 0.5 inches higher at the front, now the car sits level.
The Tein Flex Zs are "plush" compared to OEM. The rear is set at the middle setting and the front almost at full soft. Small "bumps" you can't even see are gone. The car doesn't "hop" at all (think lowered hatchback civic, 2006 VW, cheap coilovers etc). On big dips you can feel the suspension easily compressing, and slowly coming to a stop. It doesn't "buck" you around. Mid corner dips don't "roll" or buck the car much. You can definitely carry more corner speed and easier at that. It really comes down to the suspension "working" below you, allowing the car to stay flat. Ride quality is closer to Acura, BMW, Mercedes now. Another benefit is the headrest only bumps your head half as much at highway speeds on concrete expansion joints etc. This can be dialed out more by tuning the rear softer. Despite rough sections of interstate, my passenger slept for the majority of the hour ride. The ride is even quieter now, as all the bump impacts are either gone or subdued. Bumps and cracks feel more rounded off.
Cons:
1. More body roll during highway evasive maneuvers. Only noticed at the front, and it can be adjusted. A lot of that is from the M3 Performance rear sway bar (I don't have the front bar installed yet.).
2. OEM mudflaps scrape more. At the Tein recommended ride height (~ 2 finger wheel gap), they would scrape a LOT. Cambered country roads, potholes, everything.
3. Rear shocks need to be unbolted to adjust dampening. The frunk needs to be removed to adjust the front. I'm riding around cyber punk style with it out, and its difficult to open the frunk lid with everything missing.
4. The install was a pain. Not terrible, but the suspension on these cars is a bit of a puzzle compared to your entry level Japanese car. At one point I assembled something out of order and had to almost completely remove the front assembly again.
I couldn't get a socket on the "strut" top 13 mm nuts without first removing the entire assembly, including the control arm and "carrier". The carrier bolts on the shock tower need to be marked for reassembly so the wheel alignment is retained. The bolts are two different wrench sizes, and some are under the cowl requiring hand tools. On reinstall, you need to hold the carrier and control arm up to the shock tower while extending yourself up and across the fender to insert the bolts. Remember they're two different sizes too.. You really need two hydraulic jacks (since there's nowhere to rest your jackstands) to make this easier especially when trying to reinsert/align the lower bolts.
The instructions are almost useless. They don't include a lever ratio, so you have to guess how far to turn the spanner nuts to adjust ride height. No idea how far you can turn them without a safety issue or damage occurring. No mention of preload. No mention of which direction the shock top mount should be facing for the rear. No mention that you need to reuse the OEM rear spring rubber insulators. They list 4 dimensions (ABCD) to adjust for their recommended ride height, but its way too low and you have to guess where to set them at different ride heights.
Overall, better than expected. I might soften the rear a bit and likely I'll have to stiffen the front especially come summer.