I've started using a lot more frozen fish recently - mostly because we don't have a fishmongers that is within easy reach and I don't rate the quality of most supermarket fish - it never seems quite so fresh.
Generally, I have found that if you're picky about what you buy, it is very good - but I do suspect that you get what you pay for. That said, you're right, frozen usually works out cheaper, probably because the costs involved are lower and there is less wastage.
I mostly use frozen cod fillets, and although the packet says you can use from frozen, I never do. A lot of water comes out of them as they thaw, and I would rather throw that away than have it dilute my dish.
It absolutely isn't as good as fresh if all you want to do is grill it or bake and it serve it plainly, I wouldn't use it for that. But I find it very good indeed used in dishes. We're having it tonight in a tagine (so thanks for the reminder, because it is still in the freezer
), there is a fab coconut curry I do, and I am plotting to try fish tacos soon - the only reason I haven't done yet is because I we're dieting and I can't find a low enough cal recipe.
I also have a packet of frozen mackerel fillets in the freezer, but I can't seem to get DH excited enough to try them - every time I plan them, he comes up with an excuse. But I will persist!
This is the tagine: www.bbcgoodfood.com/recipe/fish-tagine-saffron-almonds
And this is the curry: www.bbcgoodfood.com/recipes/fish-mappas. I put in a red pepper too, just for a bit of extra veg.
I'll also be following keenly for other ideas!