If I were to buy one, I'd buy the other. I'd buy them in quart size. Can you get them in smaller sizes?
Quart and gallon are the only two sizes. I have used M105 but do not have a need for 205, used it once and find Menz finishing polishes much better...M105 seems to cut into the hard VAG clear much better on a DA than Menz does.
I got 12oz bottles of both from ADS. They're great for non-pro's like me who just wants to try them out without committing to buying a quart or gallon.
That is a ADS only thing, cant buy it from Megs like that, if I remember correctly he re packages them into 12 oz bottles or has some way to getting custom bottles filled.
I use both and buy one with the other unless I had a substantial amount of one product compared to the other, in that case I would still buy the other just cuz haha
I've purchased M105 in the gallon size in the past but now only really buy polishes in quarts now. Actually, that trailer I had to polish helped kill that gallon of M105, LoL.