Got the HP5370C last week. Very very nice. Not as good as a dedicated film scanner but much cheaper. 16 slides down, about 8000 to go.....
Good OCR software by IRIS (much more accurate than the sw that came with the HP4200C)
I tried one of HPs box-with-mirrors slide adapters on the 4200 - that didn't work either. Hope you get your refund!