That is a great optic and it has a long and successful history, but it could be a little tricky to get used to on a WASR if it is your first go around with Russian optics. This optic sits off to the left of the receiver a bit, is a tad high and the eye relief can be tricky for shooters new to the combination of the shorter WARSAW pact stock and the rear placement of the optic. Having said that it is a fine optic once you get used to it and will last a life time. These are military grade optics produced by NPZ in Russia, they use Zeiss glass and have been building optics since 1904. If you adjust the tension properly on the clamp the optic will return to zero without issue
The WPA PO 4x24 is the modern version of the infamous SVD scope called PSO-1. What WPA is selling is basically the PSO-1 optic but with the Universal AK mount instead of the traditional SVD mount. WPA's version also uses AA batteries, a different bulb for illumination and a slightly different finish but otherwise it's a PSO.
Here is a very similar POSP 4x24 to help give you an idea of what it will look like. POSP's are also basically the same optic but manufactured in Belarus by BelOMO instead of NPZ in Russia. During the cold war both companies produced the PSO for the Soviet military, after the breakup they continued military production but also created civilian versions as well.
The WPA uses the universal mount which is why it will fit your WASR rail. See the concepts page to understand more about how the rails work.
http://russianoptics.net/Concepts.html