I have been happily using MyMemory Pro for the last 3+ years and as a result I never bothered to download/install and/or use any other NMT. The Translated support team in ROME were helpful, for instance when I could not upload a TM through their standard process because it was too heavy.
Happily except for an issue which might be a bug (of MyMemory? of Studio?). Every time you open a project (a new one, an ongoing one, whatever), if the first segment you happen to confirm had its translation suggested not by MyMemory, but by some TM, Studio freezes and you must shut it down using Windows Task Manager. The workaround (never to be forgotten!) is, every time you open your project, to go to the project settings and to deactivate MyMemory until it is actually needed (no TM proposal).
I had a lengthy exchange with the Translated support team during most of 2019, with absolutely no positive result; you SDL people know the sentence: "We cannot reproduce your problem!". If I am not the only one to be confronted with this issue, if at least a few other Studio+MyMemory users too were faced with the same problem, then it might be worth digging into it (with the help of the Translated team) and trying to get it fixed (I had this issue with 2017 and 2019 and I still have it with 2021 too).