My understanding (in reference to Trey) is that he only using the Microverb for a reverse reverb sound during some of the crazy solos. You can see this in his various rig diagrams as well as a few choice up close shots. The remaining to Alesis (Nanoverbs) units to the left and right are for rack filler (according to StrangeDesign.org diagram).
There are full space Alesis units and the older 1/3 units. The older ones in my opinion do a decent job at some basic sounds and are relatively cheap. I was not aware Jerry use a Microverb in any form. I thought he got his reverb from a rack like the Real Tube or possibly the Twin.
The first Microverb (1/3 rack space unit) does the basics pretty well. It has a mix knob which I always felt was extremely useful.