Yes, it's true. It never estimates the infusions correctly, for me at least. It may get you to the first temp, but on a stepped mash it's off by miles.
10.71qts at 141 to get to 128 (yeah, that's fine)
6.52qts at 210 to get to 154? Not a chance, took more like 14
Glad I always boil a ton more than estimated