Pretty sure Cat C states it on the log book, it used to at any rate. Cat C is going to devalue it further than a Cat D.
From experience they tend to be 20-30% less than a non recorded car so don't buy in the thinking your getting a bargain and will be able to sell on for more. Some will say it makes no difference, but then see which car they choose between a recorded car and a non recorded priced the same.
As Nick says, if repaired well they can be fine to own but are just worth less.