I've used the 553ELX commercially for years. This is an extremely well-made body. It's kind to batteries and a dream to use for for any subject particularly portraiture since it allows you to concentrate on the subject rather than on advancing the film. Very handy, especially with an A-24 back or 70mm magazine.
It takes the full line of 500 accessories and C, CF and CFi lenses. On location, I've happily discovered it'll take more abuse than a rental car (or studio assistant). The 553 ELX is also capable of OTF metering with either the Hasselblad strobe or using the after market accessories available from outfits like Quantum. I use mine with the Q-flash and it works swell.
A bit cumbersome to hand hold with a medium telephoto, even with big paws, but still very easy to do. I suppose wedding shooters might consider using it with a monopod at slower shutter speeds.
True, it's mirror kathunk followed by the whirring of the motor is a bit noisy but I don't think any more so than my Nikon F-2A's and MD units. Ya kinda gotta expect a medium format with a motor ain't going to be as quiet as a Leica M-6. Nonetheless, I've never heard complaints that the noise is particuarly distracting.
All-in-all I rate it tops. And these days, since Hasselblad is leaning more digitally (although they still support all their earlier equipment) the prices for good, clean used ones and accessories have come way down. Truly a worthwhile value to give you more bang for your medium format buck.
Mark Feldstein, Photojournalist.