I've been fighting with siderail scope mount inconsistencies for about 2 years now and the only thin efficient about them is that they are cheap and easy to install but otherwise I'm not impressed.I have a heavily modified MTK low profile mount that I am finishing for my S308 and I am thinking that I am going to have to drill out the rivets for the original side rail and remount it with screws and a steel backing plate inside the receiver to eliminate movement and then center the rail on the mount with the optic and a laser boresighter to get a true zero so I can test if it's repeatable or not.
If I thought these dogleg units were tough enough and that they would absolutely hold zero I would toss these pieces of Kalinka Krap in a heartbeat.
I was having all the same problems you just described which is what lead to the development of the DogLeg. I found that the available products were either cheap Chinese junk or way over the top super quad rail things that cost as much or more than the rifle.
Regarding the specific concerns you have. The rail when installed and latched properly is very tough and durable, it was designed to be. If you drop your rifle on the scope as someone else suggested you will damage the scope long before any damage to the rail. Now, if someone decides to open it up and use it as a tire iron well then they're on their own. Naturally any scoped rifle requires a bit more care than a non-scoped rifle.
The zero repeatability of the rail is excellent. Again, it was designed to be. The rear quick release mechanism has a half round saddle cut into the intermediate block to locate it for and aft. It also has a central guide channel to locate it side to side. When the assembly is latched it has a very solid feel with no perceptible movement.
To verrify zero repeatability we did a couple of simple tests. With a lazer bore sight installed the rail was opened and closed repeatedly to confirm the scope returned to zero time after time. Next we took it out to the range, after all that's what matters. We would shoot a three round group, open and close the rail, then shoot another three round group. This process was repeated over several hundred rounds. Many many measurements were taken not just of the groups, but of the rifle itself to measure for any creep or movement of the rail. Some of our early prototypes didn't measure up. After lots of head scratching and development we arrived at the current design.
The Dog Leg was developed to solve the specific problem of mounting an optic on the AK while maintaining proper ergonomics. We strove to achieve this while maintaining the AK philosophy of simple, dependable, and affordable.