I can't view the video because of poor Internet connection, but from what you've said, I'd practice on turning and direction in the round yard before moving into the arena. My gelding still needs a lot of training to go in that respect (in his halter, mind you. In his bridle, his turns are lovely). He will go wherever he pleases unless I have a VERY good grip on the rein and only if we're at a walk. I can ride him down to his pasture, but it's a straight line and he knows the way. In the round pen, though, he turns in circles, always facing the gate, unless I am firm enough with my intentions. I would practice for a few more weeks and then try it out, but if your horse is trustworthy enough, then try it out. But stay at a walk for the first few times, so that you can get the hang of turning in a much larger area without worrying about being taken off with! Be safe, and have fun! Also, remember that anything can go wrong in just a halter. I know it's romantic and cool, but it is still dangerous if your horse bolts a lot or has a tendency to spook. I would not recommend regularly riding in just a halter because of the danger tied to it. Please be careful and responsible, and again, have fun!