I think their stuff is pretty great. Shipping is very reasonable and, as you said, they have a lot of very obscure Modern Russian conversions.
As for the kits themselves, I am a little on the fence. The detail level of the castings is pretty good I would say. I did have issues with the barrel on this kit, however in their defense, it was a small piece and brass looks better anyway !
The resin is very soft compared to Verlinden casting but that makes them very easy to work with. I have yet to crack a piece when trimming with my cutters.
There are also some very, very small bubbles in the casting but I don't believe they will show with paint. Not sure on that yet, but I should be laying primer on this vehicle in the next day or so (work/time permitting).
So, basically 50/50 on the SP Designs kits for now. But this is only my first one! I have one more on the shelf and two more on order from them. We shall see...