I used to use that small, inexpensive level from B Square. It sticks out to the side when mounted to the Picatinney rail. After I had used it a couple seasons I got anxious about the possibility of it getting slightly jarred (bend the tube) out of adjustment. If it ever did, it would be very difficult to ever realize that it had happened. I switched to the Defensive Edge ACI/ACD Combo Mount a while back.
When Flatline Ops' products came out I thought they were some of the coolest, functional and innovative designs I had seen in quite a while. By the way, I received a prototype of a couple neat new products from Flatline Ops a couple weeks ago. Can't tell you about them quite yet for patent reasons.
Anyway, I just went to my store's shelves and flipped the Flatline Ops Accu/Level's arm out and back a few times. It has a VERY positive detent that would resist unintended movement. Equally important -- it is VERY unlikely you would be unaware of an unintended movement.
When you change positions there is a significant CLICK sound and the arm accelerates downward quickly as it nears the default position at the detents on both sides.
You can buy Defensive Edge ACI/ACD Combo Mount and the Accu/Level Scope Level By Flatline Ops
right here in the LRH Gear Shop.