Great action cam. I use it in conjunction with the Action Cam Mini as well, creates great videos when using the video sync option in Play Memories / Action Cam Movie Maker. If you are just getting into the "realm" of action cams, I'd suggest the Mini first (since it is at a lower price point) but if you're all about 4K then this is the cam for you. I also will be headed to Japan for an extended time frame, so I figured Sony was a good option. Also cool that it integrates with my Android phone and PS4 Play Memories. I also opted to get the Live View Remote, definitely worth it. Can't wait for the update that lets me view both cams via the 1 wrist remote.
Have used all the recording modes (I have a 4K TV, as well) and have been blown away by the quality and detail. I have used the shoulder/backpack mount as well as the helmet/curved mount. I use the cams on a motorcycle, and haven't had any issues at higher speeds - wind noise though is present even with wind reduction on (not a complaint for me, I would expect some wind noise since on a motorcycle).
Typically, the 4K cam is mounted to the bike, mini cam mounted on helmet.
I would highly recommend picking up a spare battery for any Action Cam that you end up purchasing.
I own several compact action cams including the popular brands and the not so 'known' brands and I consider this camera a good alternative. I put the Sony in the top 3 action cams for its picture quality, stability, features, and waterproof housing. Where I feel the camera falls short is the price which I feel is too high for what it's used for and the limited amount of mounts. If the next version comes out at a better price point I would consider upgrading and giving 5 stars but if not. . .we'll see!