Microdol-X works great with Tri-X and Plus-X. Its main forte is that it can be used straight as a fine grain developer, or as a very sharp but soft working developer when diluted.
When used at full strength, you might notice a softening of the apparent grain. With older formulations of Plus-X and Tri-X, this was more apparent. Since these two emulsions have improved in terms of grain over the years, the effect is less noticeable. Expect to loose about a full stop of film speed if used at full strength.
Once diluted to 1+3, the fine grain effect is largely lost and full emulsion speed is regained. Because the developer is slow working and contains metol as the only developing agent, it can deliver a negative with a very wide dynamic range. That's pretty close to perfect for taming the contrast of punchy films like PanF+, or films shot in hard, contrasty light.
Newer type emulsions like TMax, Delta, and Acros don't really benefit much from this developer. These films are already very fine grained and there is little to be gained by using a fine grain developer. My favorite for TMax films is XTOL or D-76 in that order. I've never had a grain issue using either of these developers, though I tend to favor XTOL by a slight margin.
When mixed up to stock solution strength, Microdol-X should be water white. If is mixes up and shows yellow or brown, you can safely assume that it has gone bad. Dry metol will oxidize to a brown color, and the paper and foil packets of the past were not the greatest for keeping the contents fresh. The newer mylar packets are better in this regard, though they can develop small pinholes with rough handling. I still have a few very, very old cans of Microdol-X, and surprisingly, the last one I opened was still as good as the day it was packaged - sometime in the early '70's! Unfortunately, you won't see Kodak packaging anything in cans any more. It just costs too much.