[Samsung Gear S3] lucarossini:
hi there, I was in your very same position and I ended up getting and, for the moment, keeping the S3 frontier. I had an old Epson ps100 which is very good for tracking HR all day long and spotting any activity, but very bad in all the rest (step counts bad, no floor counts, horrible app with no integration with withings or myfitnesspal). Then I bought the Huawei Fit Watch, cheap and nice, but since I do mostly indoor rowing there was no way to use it but by telling it I was cycling and, then, it would make random acquisition of GPS while I was actually indoor. Then I tried the Fenix 3 HR, amazing watch for tracking sport, dedicated program for indoor rowing, but waaaaay off in terms of active calories burned, it would have me burning active calories while watching TV on the bed! I tried two different units, very same issue. On internet you'll find a lot of people having this issue with all the Garmin HR watches, and no answer from Garmin EVER.

So I ended up trying the S3 Frontier. It costs exactly like the Fenix 3HR right now, but half of the new Fenix 5. Which in Europe arrives today. I won't write a review of the watch, but just try to answer to your questions:

1. Any of you who is also doing some kind of sport activity, Are you satisfied with the watch? Is it accurate enough?

I do indoor rowing every day. Plus stretching with a foam roller. I use "Indoor Cycling" program to track the first and "Yoga" to track the second. The watch gives me the same results in terms of HR and calories than the Epson PS100 and the Huawei Fit. So I would say it is accurate, if you keep skin and hr reader clean and tight. I'm a professional photographer, and when I go out on assignments I use the "Hiking" program to track steps, HR, altitude, and to track my gps route. It works very well, even if I'm out for hours and hours.

2. Re watch apps and builtin apps, I understand that there is some bloatware, Can it be removed?

You can remove some of the original programs, but not all of them. They don't take much space though.

3. Re sensors readings and activity tracking, can it be exported to be used with other apps? Can I use orux maps on my phone and having an activity recording on the phone gather also the information from the watch?

There are other app you can use instead of the native ones, like Endomondo (which gave me horribly high calories counting, though) or MapMyRun, etc. I don't know if you can track simultaneously an activity with both SHealth and Endomondo, though. Never tried. You can surely track you gps with ORUX on your phone while using another app on you watch. Remember that in the worst case scenario, if you disconnect the watch from the phone you can use the internal GPS on the watch to track your hiking using SHealth.

4. Is it possible to load gpx files and a map beforehand and follow a route like that, offline, without a phone?

Kind of. You can load GPX files using either Komoot or Gear Navigator. Komoot is available only for users with a Samsung phone. I don't have it so I can't speak for it. I use Gear Navigator, and it works fine, but it requires the Gear Navigator Companion running on your phone. It gives you a map on the phone so you can see where you are compared to the track, but you still need your phone with you. The new Gear Navigator Standalone states it can use GPX too, and it works without a phone, but it still needs internet access or it refuses to work, so either you have the LTE version of the watch or it will still require a phone for the internet access. So, right now there is no app like Garmin ones which will allow you to have gpx tracks without maps working offline, but you have gpx tracks with maps (even satellite maps) working online. The best is I could track my "free hike" with SHealth, stop at the arrival, use the SHealth on the phone to export the GPX, open it with Gear Navigator, and have the watch showing me how to get back following my steps. That was nice.

5. Is any of the watch functionality degraded when using a non-samsung phone?

Right now some, but some of these get corrected to work with any android phone from time to time. Right now you don't have the "email" app (you can still read incoming emails, but you can't answer them or scroll through them). You don't have Uber and Komoot. You don't have the new matching themes. I can't think of other limitations right now, but probably there are. Nothing major, though, since I'm using mine since 18 days with daily workouts and hikes and all of the smart features (which are waaaaay better than any Fenix or Sunto watch) and I'm good with it.