You also have to account for Fate Point mechanics, which makes it even safer for players (and presumably other important people). It was few years ago, but I was both player and game master in WFRP - and I tried to portray magic as dangerous. All while rather 'happy-go-lucky' players treated it as safe to use in any way they wished. At a point, I really, really wanted that to be punished... but it never was. Despite of how much they were casting, nothing horrible ever really happened. So yeah, it is safer than miscast table makes it seem at first glance.
But.
BoneyM said explicitely that we are not playing by WFRP rules. He took thematics, spells, majority of setting, but not mechanics and not details. Magic that is safe(-ish) in WFRP is not necessarily safe in quest. Opposite is also true. All that matters is thematics of magic: "cast using a piece of hell". With all that it implies in narrative.
<sigh> I just wish it was easier to predict what exactly does it mean in quest. The details. Things like risk/safety, ease of casting, narrative wilpower needed to cast, limitations like spell interactions, etc.