Ugh...I look at the time in that title and I know it should be around 50 hours by now, but I just can't bring myself to estimate. If I wanted to take credit for all the time I do, I should write it down!
Working last night on some kicks. Inspired by Edson Barboza's KO on Etim, I had a light bulb moment. He delivered it by posting the rear leg and swinging the leg around. I don't know why Etim couldn't react - Barboza did catch him coming forward slightly but Etim brought his hands slightly low expecting something to the body. Big mistake.
Mawari-ura-mawashi should have that factor of uncertainty in it though. You should be able to deliver it as a low sweep, a high kick or transition it to a thrust mawari ushiro to the body without any sign of which level it is going to. Rather than posting out the leg though, which I think really signals something is up, it can be delivered with a feeling of sabaki 2, stepping in and pivoting, coming to a musubi dachi position.
The benefits of musubi as a launching pad and transition are threefold. First, rather than signalling the turn by posting the back leg in kumite kamae, the step-up to musubi suggests forward motion. This should cause the opponent's mind and guard to stay forward rather than expecting an attack from the side.
Second, indeed the step to musubi can launch a forward attack high or middle with the front leg or middle and low with the back leg in a savate oblique kick style. Depending on whether you think the turn will be successful you can still attack head on.
Finally the step to musubi allows you to feint the spin and come back with the front leg. This isn't possible with the spread leg delivery as you haven't covered enough distance to hit the opponent. You would be reaching to strike with the front leg without the inward motion of the back leg. In contrast, by coming to musubi, you close distance allowing you to pivot at the waist. If the opponent braces for the leg coming from the outside you can shift weight to the back leg and drive the front leg in a yoko or ushiro manner.
The key to using musubi is simply making the stance look the same regardless of any and all the techniques that you might deliver. The secret to using musubi however, is metsuke. If you can keep an eye on your opponent long enough (even while spinning) to determine whether his hands go up or down, whether he turns or faces forward, you can transition seamlessly from the frontal approach to the pivot and back again. If he steps back, you can lunge off the spot with a punch, driving with the back leg. If he closes, the sabaki of the motion should give you a shot at stepping offline.
I have to practice it more, both stepping up and stepping back. Obviously the flip side of stepping up in Sabaki 2 is stepping back in sabaki 6, which is a great variation on the mawari ushiro geri in case the opponent does close.