MMA cl much different then Bjj cl?

Taking up MMA is very similar to BJJ except that they add striking. You might find MMA a bit boring when they start training on grappling as they normally teach basic submissions and defenses that you are already familiar with. I suggest that you train BJJ and Muay Thai separately to improve on your striking. After you've trained on both for some time, then start training MMA to mix it up. Otherwise, training MMA makes you a half baked JiuJitsu/Muay Thai guy.