I've had the spaghetti size and angel hair size. I've eaten them with tomato sauce and a heartier meat sauce.
It's all about the prep. If you follow the instructions, the fishy smell will go away and you'll be left with a pseudo-noodle. I say pseudo because the texture is a bit off. It's not horrible if you follow the prep instructions, but if you don't, the noodles are almost slimy and crunchy.
They're expensive here, $1.79 for one package which is technicially 2 servings, and they're like 40 calories a serving. Compared to 100+ of pasta calories, and they're carb free, yeah, they're a great replacement.
Hope that helps!