It's definitely for people that value volume over quality.
The meat can be overcooked and dry - I normally go for the gammon to avoid this. The veg is normally OK as it is harder to screw that up, and the variety of veg on offer is good. The deserts you pay extra for are normally pretty good.
You see some pretty horrendous stuff there, but that is pretty much true of any buffet style restaurant. Kids doing the "dentists chair" under the soft drinks machine, people sneezing all over the veg etc.
It's not top quality food but there is plenty of it and it's cheap.
Some establishments are rough and could really use a paint job, others done up so there is no uniform standard as regards decor.
The staff in the ones I have been in are always friendly and ready to help.
So I suppose to try to answer the question is it working class ? Well it is definitely for poorer people/people pretending to be poor as it offers value. It certainly is a place where quantity is valued over quality, no culinary expert is going to go there and no one goes their thinking it is a five star meal out.
I would say it is working class in the same way Wetherspoons is. I will still probably turn up to it now and then though. It's not great for me but not unbearably awful either. OK enough food for the price point if you have a price point, which an increasing amount of people do these days.