Whelp, I installed my HKS S-AFR today. I did about 1-2 hours of research on the net this afternoon because the install and tuning directions are such crap. The wiring is actually a little simpler than the Apexi S-AFC because you do not have to splice the ground twice. It took me about 1.5 hours to install and get up and running. Then I spent about an hour tuning and setting it up.

Overall impressions:

I'm happy I traded my AFC for this, it's a lot smaller and easier to conceal and not nearly as showy as the blue VFD of the AFC. The learning sequence that is used at the beginning is a real bear to get the vehicle to idle correctly since the directions are not explicit about what needs to be done. Tuning is not hard at all, but you need to write down your various tuning points because you can only see one at a time.

Currently I have from 4000 rpms to 5500 maxed out to +50% with the stock injectors, stock MAF, deckplate in, and upgraded fuel pump. However above 4000 rpms the AFR still climbs above 12:1 and by redline they reach 14.4:1. So if you have a 98 4R with the SC you're getting pretty bad lean out above 4k.