The biggest difference between them is the PST is a true 1x, the Leupy isn't. I know its easy to shoot both eyes open up to 3x or so, but the true 1x has to be looked at in person to see the difference it really makes. The seamless stereoscopic sight picture is really nice and target acquisition speed is increased.
The PST also has zero stop, 30mm main tube, and turret rotation counter marks. I like my Mk AR mod1 3-9x really well and I wish the smaller one was true 1x (I'd probably buy one). The PST is generally considered the best bang for the buck in a 1-4x24 and can be found for $399 occasionally.