Sorry for so many threads but they are all different questions.

I have a Hero 4 silver. If you all it there had the choice would you rather buy the OSMO mobile and put the Hero4 on it which you can.

Or get the OSMO instead?

Mobile.  and mod it for the gopro/action cam.  You do end up sacrificing the app and the fun-face tracking thingy, but my use is 100% point and shoot with the steady-cam bonus.  For my use anyway, I'm treating it as a budget hobbyist steady-cam that is future-proof with higher-res cams making it upgradeable, at most my action will be casual walking and recording at the same time.  I don't intend to treat it like a salt-shaker but it greatly improves the fact of not worrying to lug a tripod to have continuous video recording that is very smooth using just one hand and being well...mobile.  I am jealous of the of Z-axis module on the costlier osmo's, just have to practice being mindful of jarring steps and maintain michael jackson'ish moonwalking while moving forward or back.

I honestly tried to get it to work with my phone, but the idea of draining your battery life plus whatever limited memory storage left for recording, and the hassle of still using it as a phone after just made me opt to try something else to spare my phone and data, and upgrade to a future 4k camera (I'm ok with the 1080p for the time being once the kinks are worked out on my setup).

Anyway, don't have my vid up yet, but I now can record for several hours continuous that I actually need an extra 64GB SD card or 2 now.  Audio is another mixbag just using the buiilt in action cam's mic (no external plug) seems ok at the moment since I'll be in a more scenic/event environment (eg. tourist on a stroll or at a crowded convention).  Like those other youtube mobile ideas of mounting a separate audio capture mic/recording solution and syncing it after is the only way to solve that issue if you want better audio to vlog/or interview someone, but almost every mobile vid I've seen, the audio is dropped out for a music track and voice over anyway so no biggie.