Forgive me for not realising that this was already common knowledge, but just so you know, I wouldn't put effort into making a video like that if this only worked on cpu's who DI towards me and let me hit them for free. That would be silly.
You're right, getting the last frame of pound to hit is pretty impossible in a real match, but as I stated in the video, it's not necessary. The pound is mainly just a set up tool to see if you can catch your opponent with the sour spot f-air in which case the Rest is guaranteed. Surely that's legit? I've used and still use the 2 hit combo version of this combo successfully so many times its uncountable because although DI could affect the direction your opponent flies after the pound, a well placed pound is fast enough and unexpected enough to catch your opponent while he isn't DI-ing (especially if you pound after a tech chase while they're getting up). I have so many replays of me executing this both on the 3ds where I discovered it and on the wii u. I even pulled this combo off on Nairo twice on stream (second time I didn't rest coz I was afraid it wouldn't kill) and many other times both in tournament and in offline friendlies.
Again, I wouldn't waste my time making a video about it, and/or post about it if it hardly worked for me in real matches against good players.