To become a professional MMA fighter you need to posses a lot of qualities like speed, strength, and endurance. Besides, you need to have a valuable skill set that you know you can rely upon to win a fight against anyone.
Training like an MMA fighter to stay fit is a great idea. And you are right, you don’t need to go to a gym to train but if you really want to get the best results, I highly recommend that you go to the gym and train there. There’s a reason why all professional MMA fighters mostly train inside a gym.
True but in my point of view if you are beginner then only you need to go for a gym . And if you are not then I don't think that you need to for a gym. You can do your workout at home.