I generally buy my converters with merits, EXCEPT for a few dedicated fire armor brutes that generally don't stray too far out of AE unless it's to get an accolade. Since they don't have many merits but lots of cash, I just buy the converters to avoid having to switch characters or log the second account.
Buying converters for converting is my main use for merits, although I will occasionally get catalysts or boosters just to finish a character NAO!
I generally subscribe to the Myrmidon and Myshkin style of playing a character all over the place and selling their drops, after conversion if needed, as they level up. Once they get far enough along the incarnate path that I consider them "finished" and I move on to my next project, I may assign them to buy and sell a certain thing and then visit with them every few months to collect, craft, convert, sell, and set up new patient buys.
That's just not procto-logical!