Microdol-X has an additive (the 'X') that prevents dichroic fog. Without the X the old Microdol metol/sulfite/chloride formula is unusable with any modern film - where Tri-X is modern. I suppose it might work with Efke or whatever Comecon film is still in production.

The 'X' is generally held to be a mercaptan, possibly aminopolycarboxylic acid, or as Kodak so helpfully states in their patents "... a sequestering agent selected from the group consisting of oligomeric carboxylic acid substituted hydrocarbons ..."

I emailed Photographers' Formulary about stocking aminopolywhatsit but never heard back. Maybe I should prod them. But as I bought a 10+ year supply of M-X when they announced discontinuation I'm not in any hurry.

TMax-100 in Microdol-X has about the same level of grain as Tech Pan, though it doesn't have TP's gradation wherein 35mm can look like 4x5 with modest enlargement.