I have the MK-II guide and I've used it for some time. I also have an eclipse/vice style guide. I much prefer the latter. Smaller chisels are difficult to keep square in MK-II guide and it's more cumbersome to use and setup. The problem I has with my vice style guide was that it was hard to get the chisels to set into the dovetail shaped clamping area. I just got a new one (from LV, ironically) and the chisels seem to lock into place with less trouble.
For plane irons, the eclipse style guide is even better. Because it has a small wheel in the center, it's pretty easy to add a camber to a plane iron. This is not simple with the MK-II. A different wheel is available for to MK-II form cambering but I've never used it and don't want to spend the money.
When I regrind I like to use a guide to reset everything to square and a precise main bevel angle . When I hone and re-hone, I've been mostly doing it freehand. I've also been experimenting with using a single convex bevel which can't be done with a guide. FWIW, I think I prefer the flat primary + micro bevel but the jury's still out.
Either way, I'm probably going to retire the MK-II entirely and maybe sell it. It's too sophisticated and too bulky for me. IMO, guide or freehand, sharpening should be simple and routine.
-- Dan Rode
"We are what we repeatedly do. Excellence, then, is not an act, but a habit." - Aristotle