Well, I got the final piece of the puzzle for my PS90 USG. Consider this a review.
I installed the REM 3Tb myself. I did manage to mess up making the hole too big and using a slipshod patch work of electrical tape and resin. In the end I managed to use the resin as a putty and fill in any holes around the tape. But it works.
Handy little piece of equipment. Slapped it on the PS90 and had a blue reticle in one turn of a dial. Adjusting it is a snap and completes the furniture. The knob for operating the various 1-11 / 0 positions is stiff. Enough that it won't get bumped into on/off and good for travel. Taking the top off is easy enough to replace a BIOS battery (CR2032) for its power.
The REM 3Tb mounts in a recepticle that I see no use for. Granted it is a sling well, but I haven't seen many people make use of it.
Was in phone contact with chris during the time I bothered him and great customer service. Pointed somethings out that might help in the future.
Only complaint I have is that there is no option to have red and green and blue in same package. That is more of an LED thing though.
The rails I got from mptoledo would have interfered with the REM 3Tb because they go back over the sling well. I thankfully had a family member with some machining equipment that I was able to shave off 1/4-1/2 inch off the rail to get clearance. Something to keep in mind if you have rails that go back. A dremel will accomplish the same thing.
Using a blue reticle with a red laser looks kind of neat. Almost reminds of the red, white, and blue...