Re: USO TPAL
Honestly, I had two new 3.2-17 USOs side by side, one 44mm ERGO, one 44mm TPAL.
In lowlight, The TPAL was noticably darker.
The TPAL required more fine adjustment and was less forgiving.
The TPAL had a longer turret block and required more rail to mount it on, wider spacing of rings, and consequently less forward and aft movement to adjust the position of the eyebox. Not a big deal but worth mentioning if you are putting it on say something like an M14 where the rail is extremely short, or using a unimount such as the Spuhr (which is not compatible).
The ERGO required the reach.
A flip up cover on the ERGO rotates with adjustment. So you have to place it on the scope at the right clock position so you don't have to take it off when adjusting for parallax.
Honestly, if I were to order a USO again, it would be an ERGO. The reach is a weak excuse to want the TPAL over the ERGO. By that logic, no one would want to do positional shooting because it required them to hold the forearm and get off their belly or stool.