700 mv is not that much. It's not even enought to light up an LED, although it's a bit higher than spec, the chips will be fine with it, it's still a pretty low voltage
Compatible means working effectively on Samsung, Hynix and Micron RAM with good timings, and only 700 mv voltage, on some good RAM chips, voltage can be dropped lower than 600 mv
And what if I told you than NO actual cases of FS corruption were found during testing? Remember, 4IFIR uses lots of custom optimizations and even a custom build of Hekate called 4ekate
The voltages are almost stock (slightly higher) and the timings are short, the performance benefits are huge, and it works on most of the Mariko consoles, no corruptions