i have some classes on the vedic mnemonics but haven't used them much. i can say that the roman room method was a lot faster for me at internalizing numbers than the school's reams of arithmetic work, though. at least until i stopped doing math for a year or two and lost it again. in school i would just make a multiplication matrix on a sheet of paper and reuse it. it wasn't "a calculator" so they couldn't do anything about it. they were so mad.