Install was a bit nerve wrecking, but worth it.
The screw does not move on my unit, maybe Engl has added thread locker such as Loctite 222. I have not checked.
It fits under the trem springs in my case. However, this is going to depend on the thickness of your sustain block. You can try sliding a 3mm hex wrench, under the springs of your guitar, to check.
Overall I am very happy with this product, but I wish 2 things were better.
1. It is stiff to lock and unlock
2. The provided screws are magnetic, which is acceptable, but not desirable or necessary in this application.
Compared to a Tremol-no, this is the better product. More dependable, does not unlock itself.