My car is sporting one. I found that it partially fixed the missing/flat spot problems through the high rev range and increased power due to the alteration of the previous very rich air/fuel ratios (at that stage running 12 psi with aftermarket intercooler, exhaust etc – my standard R33 computer going into super rich air/fuel ratio mode). Although I feel the missing problem was a combination both the rich air/fuel ratios and faulty coil packs (now they are painted in a pretty blue heat resistant paint and work like a dream).
I wouldn’t be surprised if I gained at least 15rwkw after getting the SAFC tuned, and the power delivery was much smoother as Leech has said above. As I picked mine up second hand for a relativity cheap price it has been a very good value for money modification providing both a good increase in power and power delivery. Hope that helps
EDIT: Actually from what I remember (ive got a bad memory though ) the dyno run before it was tuned was getting close to 190rwkw (somewhere in the high 180’s at least) and now after the tune getting 210rwkw. Quite a large increase in power…