I posted this on the "new axis axle" thread, but it really belongs here! So don't be confused by remarks that fit that other thread.
I got the Centramatics. I was surprised to see that there were two different types (I ordered before I saw Davidz71's post). The one with the offset is to allow for disc brake caliper clearance. Either style fits nicely inside my 15" X 7 alloy wheels, even with two layers of weights on the inner surface (the other wheel had three layers, but I had the mechanic move the third layer). Three layers was just too close, although it may have barely fit (no contact between Centramatic and wheel is allowed--I interpret that to be "or anything on the wheel"). The Centramatics can go on the hub "face out" or "face in". I think this might be important if you have steel wheels, but the alloys all seem to have the right depression of the "spokes" (the flange part of the wheel) that allow plenty of room.
What's the down side. Well, none.
Except for me, that is. Remember my axle was manufactured for a lower weight rating than needed, so the the swing arms are up a couple of degrees? This put the shock near its upper limit, so I ordered the 555002 (about 2" shorter) to make sure the shocks didn't bottom out if the axle did. I only intended to use these shorter shocks until I got back to Colorado from Vegas. When I got home, I discovered the shorter shock didn't allow the swing arm to swing all the way down, so I had interference when trying to remove the wheel--had to pull the wheel off, then the wheel got caught on the top of the Centramatic, so had to hold the wheel up a little and wiggle the Centramatic off the studs. Not a big deal, just an aggravation. This won't happen with the normal shock, since the arm will swing down far enough to allow easy removal of the wheel.