I go to OTF and I think it works for me but I’m not using it to build muscle or lose weight. I just won’t make myself do cardio otherwise. I will say, I have visible muscle from weights/Barre and am thin but there are people like you mention who don’t “look” in shape who absolutely beat my ass on the treadmill and rower. They are strong and have tons of cardio endurance.

OTF is really hard on your body and can easily lead to you over-training and getting enough recovery time. Be careful with this.