They should be accurate enough for most purposes. For anything that requires truly extreme caution with dosing (anything with a single digit mg dose or anything at all dosed in ug rather than mg) it's necessary to switch to liquid/volumetric measurement which BabylonBoy briefly outlined up there. You actually reminded me that I need a new set of scales so just ordered some myself: £10.99 inc p&p. If money is not a problem then by all means spend a couple thousand on a set of lab-grade scales but, unfortunately, that's a bit beyond the reach of the average drug user.
As for RCs, aMT isn't really an RC in my book. It was a prescription antidepressant in Russia until the early 80s and was used extensively in various medical test situations back in the 50s/60s (Ken Kesey wrote One Flew Over the Cuckoo's Nest based on his experiences as an aMT test subject when he was in a mental institution in the 50s for extreme depression, he called it "The Rolls-Royce of Psychedelics" which is quite the recommendation from the Merry Prankster himself

). The term 'RC' is very loose and nebulous - bordering on meaningless almost - but is generally used to denote any drug that isn't widely available on "The Street" - especially if its name looks like somebody spilled a tin of alphabetti-spaghetti and decided it'd make a good name for a drug.