Rega TT PSU..... one or two buttons ?


I'm thinking of buying the TT PSU as an upgrade for my Rega P3-24/Exact 2 front end. I've seen different photos on the web, and it seems as if there are two versions of this unit. One has one button (33 1/3 - 45 RPM), and the other has two buttons (Power and 33 1/3 - 45 RPM). Is there a difference ? Are there actually two versions of the TT PSU available ?
Also, what are the thoughts from those of you who have the TT PSU ? Is it a significant upgrade ? Thanks a lot.
adam18
Thanks for the response Miner42. Your response has somehow increased my chances of ending up with the P5 although the P3-24 with TT PSU was initially in my shortlist.
Okay................can somebody explain why the TT-PSU will make the P3-24 sound better ?? I don't want a theoretical answer, but rather a simple description of an audible improvement. My P3-24/Exact 2 sounds pretty incredible right now, through my Rogue Audio Cronus and Vandersteen 1C's.....what will the TT-PSU do to improve the music ??
TT PSU reduces motor vibration. Any upgrade like that will give the music a more relaxed, precise presentation. I use a P5 with TT-PSU and the difference is there but not huge. A quality cartridge will make a bigger difference IMO. In Canada the TT PSU was $400. I use an APC Back UPS which frankly makes as big an improvement and costs only $80 here. I would have spent it on a better cartridge first if I was to do it again. It does give you switchable speed so I do not regret getting it. Might make a bigger difference on your system than mine depending on its resolution.