Those B+M key M.2's they're SATA3 600MB/sec. If we take that and put inside a USB stick enclosure would it run under USB3.1? Are the B+M M.2's only work up to 600MB/sec?
Don't know. The fastest I could achieve with the mentioned enclosure with USB3.0 was 334MB/s read and 311MB/s write under Win 10 (UASP enabled).
It was a 256GB Transcend MTS400, M.2-2242, SATA 3 (rated 560MB/s read, 460MB/s write). The 512GB version should be ~20% faster (be aware that the newer 2280 doesn't fit in this adapter!), the 128GB (and below) are slower.