I agree it's a great tool, and I like the idea of the app. Now if I can just get myself to remember to use it. My iPhone sits during every class in one of those convenient locations you mentioned. Sometimes there's even a tripod sitting next to it. And yet, I keep forgetting the damned thing is there. I think I enjoy classes too much.Didn't realize there was a site subscription. I've been using it for about 6 years without it. I've saved some videos to my computer by exporting them to my camera roll (or whatever it's called) on my iPhone. I'm sure there's a way to email the videos.
It doesn't have to be a long video session to be effective. Record a form or two (if you do forms). Record a few minutes of sparring.
You don't have to do everyone the same day/class. I'm sure you know your students well; record one for a few minutes, then after class review it with him/her. It realistically should only take a minute or two of sparring to see the mistakes they're making. It's not like a pro fighter/athlete analyzing hours of film.
My idea for someone like you is to keep your phone in an accessible place and grab it when you have a chance to do so. Record for a minute or two and show the student after class. Most students make the same mistakes over and over in sparring, such as posture, timing, etc. It gives them a chance to see exactly what you're seeing.
A phone is good enough. An iPad is better as the screen is bigger. I haven't put it on anything other than my iPhone, but as with other apps I'm pretty sure I can put the app on my iPad that has the same Apple ID.
Sorry if it sounds like I'm pushing it on you. It's just a great tool that's not as intimidating nor difficult as you may think it is.