Before you invest money and a lot of time for studying GTO, keep in mind, that GTO only making sense on the middle or high stakes poker. (It's an opinion of couple of serious middle stakes poker coachs, which opinion i agree and share.) Exception is, when you suddenly meet a very good regular at micros/low, who been studying GTO too and played with you already reasonable seize of
hands. But how often that happens? Not really often. Mostly you are surrounded by fish and donkeys at micros, who have not a slightly idea even about meaning of GTO. And against such players, playing GTO concepts can be even counterproductive, as you are loosing value a lot of the time. The best strategy against them, being more simple, straightforward, collecting money as much as you can from your good hands versus telephones and trapping aggro-fish with some check-raise tricks at post flop. And if it should happen, that you meet a micro-reg who is aware of GTO, simply change the table in terms of increasing your profit, don't clash wish sharks, it's not profitable on a long run. If you meet such regular in a Tournament, try to play with him very conscious, try not be involved in huge pots. Better stay away from him, as much as you can.
p.s. However, don't get me wrong, in general i think, that GTO conceptions are must to learn for any serious regular player, in terms of beating middle and higher limits. Because it's the place, where the problems start. First and foremost, higher limits means less fish and more solid players. It make the game much tougher and demanding much more intellectual work at play. At some tables it can be that, there are only like one or few fish, haunted by a lot of sharks. And you are kinda forced to play against sharks a lot and you got to be better, than they are, so you can make profit on a long run and keep climbing the limits further.