Is it mixed automation?
I'm just not so sure that having it in ARM as "protection" is really as safe as you make out.
The pilot "knows" it's in ARM, so may be expecting it's protection. That could be more dangerous than it's worth. I consider it bordering on mixed automation, which has already killed two 777's.
Sorry, I'm a big fan of "all on" or "all off". At least you know where you stand if the situation suddenly goes pear-shaped.