well, it is a "cheap" card, but it is a sandisk card, from a reputable seller. (we don't have authorized resellers here i believe)
and of course, i tested extensively before any "real world" usage.
luckly, the dr-70d does appear to have a decent buffer, so it writes for about 1/4 of a second every second (using 4 channels 24bit/48khz) on my "slow" card
so, audio is very low-demanding on the card speeds. and for what i see, the incompatibilities where never about speed, but bad design/firmware on the 70D, that also i believe was somehow "fixed" on later firmware updates (i got the recorder after the initial problems on older firmwares). maybe if i record in 96/24, a faster card would be wise.
i tested it with all brands/models of cards i have, and all of them worked perfectly. even a few micro-sd on adapter.