I always declare kava. I used to do a fair bit of international travel - I would not be concerned about TSA on domestic US travel, at the end of the day you're carrying something legal so it might cause a fuss but in the end, no problem.
Overseas customs is who you have to be sure about. I tried very hard to find out the rules about kava in HK and Macau. They replied to me, but it didn't help much. In the end I declared by Paradise extract in both places. They were baffled, and eventually I explained it as "relaxing chocolate" when it was clear "kava" meant nothing to them!
Unfortunately a lot of my travel goes via Singapore. I am fairly sure it is classified as a poison there. Don't mess around with Singapore and this stuff. It is not worth the risk in any way. So don't take kava through Singapore. Malaysia and Indonesia are probably on this list also. India? I am not sure.
I had a funny experience flying into Suva once. I bought Fijian kava in Tuvalu (I don't think they can grow it there, or if they can, not much). We still had some left over. When I declared it to customs on entering Fiji they were overwhelmed with excitement and hence followed a nice long discussion about kava