Another Bonmusica fan here. The killer feature is the ability to
reshape the metal bar to fit to your exact preferences. (For example,
if you object to the hook over the shoulder and want more freedom, you
can just bend it out of the way.) Almost like having a custom rest made.

I found that once I got it adjusted to my satisfaction it assists me
in balancing the instrument naturally much as I would do without a
rest, and doesn't tempt me to squeeze with my head. In fact it
(together with an Ohrenform chinrest)helped me cure a squeezing habit
developed while using other rests.

Steve LaBonne