I also have a 1997 6MT and I recently had a ClutchMasters FX350 clutch/flywheel combo installed in anticipation of going FI down the road. I had considered the SOS clutches, but a number of recent horror stories (along with personal recounts of guys highly respected on this forum) made me ultimately decide to go with ClutchMasters.
The only review I found of a ClutchMasters clutch for an NSX application was RYU's review, which was very favorable. However, his review was of the FX300 which is made of different material from the FX350 (FX300 = carbon/kevlar, FX350 = "Fibertuff"). Coincidentally, I have plenty of personal experience with the FX300 as I had that clutch on my old car (350whp supercharged TSX) and I absolutely loved it. The one thing to remember about the FX350 is that it's a segmented puck clutch. This style of clutch typically holds more power than a full-faced disc, but isn't as on/off as a full puck clutch. Essentially, it's designed to be a hybrid of the two styles.
For reference, I weighed all components and here is what I found:
OEM (97+)
clutch + PP = 14.0 lbs
flywheel = 30.55 lbs (!!!)
ClutchMasters FX350
clutch + PP = 15.10 lbs
flywheel = 12.35 lbs
When the clutch/flywheel was first installed, there was a bit of chatter when starting from a dead stop. However, that was to be expected when going from a dual mass to single mass flywheel (and shedding over 17 lbs in the process). I now have just over 900 miles on the clutch and most of the launch chatter is gone. Like most lightened clutch setups, you just have to give it more throttle at launch to alleviate the chatter.
Pedal pressure is just like stock, no discernible difference to me. The clutch engagement is a bit stiff but getting better with more miles. It grips really well, yet it is still fairly easy to modulate. However, I probably wouldn't recommend this clutch for people who drive their cars in stop/go traffic as I noticed some bearing noise with repeated engagement/disengagement cycles. It doesn't happen in city driving where you're driving in 15-30 second intervals, but I was stuck in one or two heavy traffic jams on the highway and that's where the whining noises started popping up. I could tell the clutch doesn't like to be slipped excessively, but since 80% of my driving revolves around backroads on the weekend this isn't an issue for me.
Regarding your concern about an aluminum flywheel making noise, I haven't noticed any. I also worried about that initially, but it really isn't an issue at all. Both at idle and driving around, the car sounds completely stock.
To summarize, I love my ClutchMasters FX350 + aluminum flywheel combo. As with any performance-oriented clutch setup, there is an adjustment period. That said, it's as close to stock as can be while providing all the benefits of higher torque capacity, reduced rotating mass (acceleration is noticeably better), and far less rev hang (much easier/quicker to revmatch my downshifts).
