I use it or 6.0.x when I need 3d on XP/2003 VMs, but on my server I need a version that runs side-by side with vmware and Hyper-V (technically vmware and vbox runs inside Hyper-V, but from the user perspective they runs side-by-side), which means at least 6.1.18 or so (probably 6.1.28 is the most versatile and problem free version yet)
If they had released the legacy 3D for XP et. al. as a plugin for the later versions, I'd have moved on. 5.2.45 is most stable and fast on my PC (AMD FX, Windows 7). 6.0 BSOD'd my Host. Didn't try 6.1 nor 7.x yet, which officially abandoned Win7 as Host.
At least they deprecated a feature but users are free to use the old versions at will. MS REMOVED the RemoteFX from people's servers via the monthly "updates" (maybe a graphic studio with dozens of clients), and they did that BEFORE providing any kind of similar alternative. Perhaps do you have a link to the 5.2.45 extensions? I had it but looks like i deleted them by mistake.