While not a true Hinckley, they are well made boats, though I never liked the pinched stern treatment of the 40'. I think Hank Hinckley designed the boat himself, where most of the other Hinckley models have impressive design pedigrees: Sparkman & Stephens (Pilot 35), Bill Tripp (B-40 & H48), Ted Hood (H43), McCurdy & Rhodes (SW-42, 43, 51, 52, 59) and Bruce King (SW-70).
If the boat is well maintained and the price is good, it may be a good value, provided that is the kind of boat you're looking for. Like most old-school boats, these will have small interiors for their LOA relative to modern boats, but will sail well and have a nice motion.
If you're serious, you need to look at the boat, spend a couple of hours aboard, crawl thru the unfinished spaces like cockpit lockers and check the workmanship. Sit in the cockpit and lean against the cabintop. Is it the right angle for you or the bride to read a book?
T37's link has lots of good info, there was also a review of one of the OC40 in Nautical Quarterly many years ago. I know I have the article somewhere, PM me if you want it.