SSD
GPS Pilot III all the way for Yaks. Very user friendly, excellent moving map plus all other features from their larger model 195. Fits very well on top of the coaming of the 52. Do not rely on the velcro. You will regret it first when it comes off and sails out your partially open canopy (!), or worse, disappears below your seat where it could foul controls...
Instead, simply screw the Pilot III bracket onto the annuciator light panel. Fits perfectly, very secure, and not in line of sight too much.
For the Yak 50, we built a bespoke bracket, which fixes onto the top of the coaming, but bends down to position the unit out of the line of sight along the top of the engine. This is just a reflection that the top of the coaming in the 50 has no annunciator light panel, so cluttering it with a GPS unit just reduces forward visibility. You could of course make a similar bracket for the 52. Also, you can feed the external aerial around the side of the cockpit and set it up behind the passenger seat. Although I will say that I have never had a reception problem with the GPS III just using the standard aerial - lots of clear glass above it in the Yak cockpit !
A word of caution on the GPS III: rarely, they have a software glitch which turns it off repeatedly in mid-flight (!), despite having fresh batteries. Transair replaced mine no questions asked. Likewise for a friend of mine who suffered a similar problem. No reoccurrence in either replacement unit for the last 2 years.
Finally, you can in fact connect a GPS to a Yak 52 or 50 electrical system. But I don't know exactly how to do it ! Meanwhile, you will use 4 AAA batteries every 6-8 hours or so.