I started doing it again when i hurt my wrist for about 2 months, and theres some really useful stuff (there is also alot of crap too) if you can find an ITF school go there and don't do WTF. Also for the guy earlier in the thread, in the U.S. you guys have ATA Taekwondo which is the Mcdojo of the world, avoid that at all costs. The main thing that pissed me off at legit WTF schools also is that they have been teaching the same fukin shit for the last 20 years, and are so narrow minded its ridiculous. My teacher talked about bruce lee like he is a god. Our TKD vs any other martial art convos are always funny too, he basically uses the kick in the balls or poke you in the eye argument everytime.
Still i think TKWD with Muay thai is deadly imo. ITs just another arsenal to be used in mma, especially if you have with a sick guard. Kwonkicker has a really cool channel where hes adapted a bunch of taekwondo kicks for muay thai calling it "taekwondo kick boxing. also jason first page, (i know its old) but david loiseau is one of the first guys in the UFC to use TKD effectively in MMA.
This vid is from him in thailand, you can really see how kwonkicker uses his TKD base to own the muay thai guy, and its mainly because the only defense from kicks the thai guys know is checking the leg, (leaving there stomach area wide open, which is jizz in ur pants for TKD guys, You could make the same argument for an average well-rounded MMA guy, whose only training train muay thai and wrestling bjj etc. who would not know how to defend the TKD kicks. joe rogan talks about this alot too, saying you should train TKD once a week or incorporate it into your training to learn the few devastating techniques for mma.