Looked at them this morning. They look OK but quite bulky rolled compared with our thermarests. They're about a fifth of the price though, so if you're not pushed for luggage space or back-packing...
It depends how heavy your are. The heavier the person, the more likely they are going to feel the floor under them, especially when lying on their side.
I have one, I used it last night in fact. (I bought it in a previous Lidl camping event.) I think it's great, I'm not a lightweight person and I have disc problems but I always sleep like a log on it, often better than I do at home.