I have just installed the Sleepy Time Records VU meters to compare against the others. In my case I have got three sets now with PSP and Klanghelm as the other two.
The Sleepy Time VU's are very good and are perfectly accurate. The rise time is very close to both the real VU's and the PSP meters. The only slight difference is that the way the real VU and the PSP comes to rest and here the fall back is a little more graceful with the real VU and PSP VU. Sleepy Time VU's tend to land back in the rest position in a slightly different way but it is very minor and as they are free that is excellent.
You don't seem to be able to adjust the integration time as per the PSP (and Klanghelm) meters but it is obviously set very close. There are quite a few other things you can do in the Sleepy Time Mono/Stereo channel though which is certainly a lot more useful than other VU meters alone.
All three VU meter VST's are just DLL's you install and scan into the appropriate folder. No Ilock or anything required. There seems to be 64 bit versions too.
Update I have done some further testing and I have discovered that while the PSP meters read the correct level with a continuous tone they read high by about 1 dB with music. ie they are tending to overshoot very slightly. Changing the integration time in a way can lower the overshoot but then the ballistics are slightly more sluggish as a result. A better way to get the PSP meters to match the real VU's with music is to set their ref to a level 1 dB higher. eg I have got my real VU's set to -14 dB FS so the PSP meters have to be set to -13 dB FS to make them not overshoot.
The Klanghelm meters do not overshoot at all and reach exactly the same level as the real VU's do with music and the continuous tone. I would say the Klanghelm meters are a little more accurate all round. The Sleepy Time Records VU's also do not overshoot either. They are spot on. They differ only in their last part of coming to rest ballistic.