It is slightly bitter. But other than that it is fine to swish with. I like the taste of Udo's better because it is very nutty (the traditional Udo's that is). Flax is sort of bitter also.
But lately I've needed to use Oregano Oil, so that makes everything taste sort of bitter. I can't stand the taste of OO, but at least I know I'm getting a good dose of antibiotic.
If you want something that tastes good, you should check out the Macadameia Vanilla Oil my husband bought. Now that it some decadent oil. It almost feels wrong swishing with it....and I always swallow a bunch when I first put it in my mouth. Oh heck, forget the swishing, I'll just chug the stuff....