Underneath Piano V is Modartt's Pianoteq engine, though it looks like it is Version 3, so probably doesn't include most of the recent improvements in sound. I do like Piano V and to be honest I think it would be fine for a lot of people with a decent reverb.
What is interesting about Pianoteq is how different the piano models sound. I wasn't really expecting the level of difference that you can here.
Even though I love Pianoteq, my go-to piano is still SS Signature Grand and Noire, as I love the out-of-the-box sound. Part of this is I also haven't spent enough time getting Pianoteq into a room sound I love. I am very tempted with the Berlin Studio reverb for this reason, and that I am sick of have loads of mics I need to blend.