I recently bought a UFO25 that Groovy was selling for his brother. The amp is beautiful like you said, more striking in person. I was previously using a UFO with 25th mods and really liked it, I thought the transition would be a simple one, nope! I also bought the full Cryotone compliment for the UFO25. When I first got the amp I decided to just transfer the tubes from UFO and use the Cryotone VR tubes. Mullard GZ33, SV83's and an Amperex 6DJ8. The sound was good, and sometimes great then sometimes just not right. This is where a long string of mistakes and assumptions occurred. I went forward with the assumption of "if something isn't right then look up the chain for the issue". I knew my turntable was setup good, the tubes in the ZP3 were to my liking, so I went nuts with rolling tubes in the CSP2+. Again went though good, bad and ugly. At this point I put the CSP2+ back where it was. I now dove into the UFO25 tube rolling. I replaced the Cryotone OA3 with a pair of OB3's. Better, much better, but still not happy. Rolled the input VR tube and that wasn't it. In the UFO I REALLY liked the SV83 and stubbornly ignored rolling them, they just can't be the issue I kept telling myself. One night I finally put in the Cryo 5AR4-WC v2, EL84-WC and ECC88-WC. B I N G O ! ! ! It was the SV83's that just didn't work for me in the UFO25. I've kept the Sylvania OB3's and a Raytheon OD3, the Cryotone VR tubes just don't sound great to me, with them in the sound is too edgy, sounds didn't "end" well, ragged and edgy. The sound also leans a ton towards bright which is no good for me. The sound just had a huge bump in the upper mids into the highs, some may like that, to me it was quite fatiguing.

I felt the same as you about the "tiny" 5AR4's, I liked the sound of the larger tubes but for my room, system, ears that tiny 5AR4 works better than Mullard GZ32 or GZ33 which really surprised me.

As far as going full compliment of Cryotone, my personal opinion is the rectifier, output and input sound great, the VR tubes I wouldn't recommend - BUT, they may work for you.

Good luck getting it dialed in, once you get close the experience is jaw dropping!