They make you feel better as in more cosy or whatever but it doesn't actually take away the pain, atleast not for me. The best thing is just to take painkillers
To answer the OP, sometimes it works and other times it doesn't. I usually stick with some paracetamol or ibuprofen, they work wonders. Mind you, it probably best to avoid taking any drugs if you can, but mine(cramps) are just deadly and only for the first day or so. As for brands, I don’t know.
I use heat packs for period pains and generic stomach cramps. They're a good substitute for hot water bottles when you're at school or another place where you wouldn't have access to a hot water bottle or it would be inconvenient.
Curaheat are good- I thought they'd be expensive because they're the most prominent brand really, but they often work out cheaper than the lesser known ones because you get quite a few in a pack. I would have a look in your local chemist's though- they'll probably all be in the same section so you can check out prices.