A con. Go to the nearby Grosvenor museum which actually has Roman relics, is free, warm, interesting and accessible.
The visit to the Dewa place was one of the worst tourist experiences I've had. Cold and dirty too.
There is a wee place next to the Grosvenor museum where a tour guide gave an excellent hands on guide to Roman armour and helmets and horns etc. But please don't give the Dewa money - I feel conned.