Flows on Hope from RM(wheelpro) here too, just done a week touring on them which ended with me taking the XC bike down the Fort-william DH track 😈 Not even a scratch, despite smashing the rim off rocks a load of times (light xc tyres are not the best choice for that track).
Ive got D521’s on my DH bike (had them for years) and they are still solid. Used 819’s for bit a few years ago (for ‘FR’ riding) and ended up with some dings in the sidewalls, nothing big enough to cause the UST to fail tho, and the wheel did stay straight, but i dont think they are as happy being abused as the D521 and Flow are.
Rich.