I purchased a 555ELD earlier this year. Had been searching for a 501cm or 503cw but when I saw the 555ELD for 499 GBP I could not resist, since it has all the features of the beforementioned and then some. Added a magazine for 99 GBP, all in like new condition. Surely it depends on the shape of the setup but 600 GBP sounds like a bargain to me. After I have used it for some time now I can say the 555ELD is a great camera, especially for portraiture. You can place your left hand at the focusing ring and your right hand on the release button all the time, shooting along unheedingly. My film consumption has definitely grown since I own this camera :-D
I used a Rolleiflex SL66 for some years and though I donīt do much portraiture it was always a bit awkward. Now I never miss a shot.
The Rollei on the other hand has benefits too, I wish I could have her High-D Screen in the Hasselblad, since the Acute Matte D is not quite as good, but close. The motor and battery housing does make it quite heavy though and itīs not a camera to carry around all day, except maybe when using one of the smaller lenses like 60, 80 or 100mm.