The 52 has been out quite a few years now and personally I think it's a hidden gem within the Diana range. It achieved sales but perhaps not quite as much as Diana has hoped. Though not so bad as to drop it from range as it appears to still be there in the model 48 guise.
Way more stroke than is ever needed here in the UK so my Firebird model came sprung with a miniscule spring back in the early 90s. Wish I'd bought the .177 model actually. Many tuning houses recognised the power potential of the gun back in the day and most had their versions of it. I think Venom and Robb had 25 ft llbs out of theirs. They can be short stroked I'm sure to something much sweeter to make use of their inherent accuracy.
I have moved onto the Airking semi recoiless version of this family of guns and use .177 and .25 versions to good effect on the local grey squirrel population. Albeit these guns come with a weight handicap. Still excellent hunting weapons though. The .25 version knocks squirrels into next week whilst the .177 version's accuracy allowed me to confidently take a squirrel with a head shot at a range I wouldn't have thought possible. They do inspire confidence with their accuracy.
Good luck with your project.
Dave