I have one..
i use is quite a bit and the files are awesome. I also use a P25+/P30+.
it's cheaper because of the following..
1. It's slower, solwer to process, slower to preview the shot eyc.. just slower (often not a bad thing).
2. It's files are converted to 14 bit MEF files not 16 bit, however they are great MFDB files and no editor here in NYC can tell which DB I shot on.
3. Screen is cr@p totally cr@p but hey you all knew that.
I think the backs are a steal and a great 'in' into MFDB also a great back up, We were shooting a fashion spread recently out on the saltflats in Utah, the P30+ packed up (ultimately a battery problem) but the mamiya back worked and worked and worked, so much so that i used it on my 'day off' down in Bryce canyon..
Fashion images here (recent 1)
http://www.stevebrickles.com Bryce stuff here (Utah)
http://www.brickles.org
Buying a Leaf Aptus 22 or a P25 gives you 'in the real world' a faster back to work with, with industry standard file types and ..'slightly' better files but that's picking hairs and is a whole different debate.
A new Mamiya back at $3700 is a deal... but so is a SH back from Steve at $7000... BUT if you've only got $3700 .......
S