Quite a bit of discussion on here about it:
http://www.airgunbbs.com/showthread....ght=compressor
Bit 50/50, some people love the idea but many like myself prefer the assurance of the drive bottle for a dry supply. There are a few folks on here who use them.
Also if you're having a 12L 300bar cylinder filled for £7 you need to refill your rifle with the compressor over 2500 times to break even on cost. I rather suspect the cheap compressor will have died or need servicing by then extending that count further.