I have absolutely no eperence with the RC Booster, but I've heard great things. I have owned the pickup booster, and while the boost works great for a clean, huge boost, the "eq" or resonance filter does absolutely nothing. I tried it with different guitars, different amps, different pickups, all to no avail. It is a fantastic clean boost though. Very similar to MicroAmp or MC401 booster, which is why I sod the SD, since I already owned both of the others.
Yes I did have it first in the chain, and the switch never made any difference. Like I said, it was a good clean booster and have no real complaints about the pedal, it just didn't do what it was designed to do. YMMVDid you have it as the very first pedal in the chain? The switch does nothing unless it is the first pedal in the chain. I have the SD and find that switch makes a big difference. I don't like it on the modern setting but it sounds great on the other two. I have owned an RC as well which I found to be very sterile sounding, many others agree. It's great having the separate EQ but overall I find the SD to be a really nice transparent boost and the switch can really make my singles sound like low to mid output humbuckers.