Here is a professional swimming talking, so the watch is very lightweight and very easy to use. You can control you music by using phone, you can take phone call, receive notifications and a lot of different stuff that makes this buy very worth it.
The swimming pool mode is good, although if you're getting short rest intervals it may confuse and put it all together, miss one or add one lap. I find the wrist heart rate monitor very precise but you would need to use it very tight so it can read it better.
Talking about the Open Water Swimming mode, the GPS was nearly perfect. I do recommend to no push your bottoms in the salt water because it could ruin the wast.
I also recommend to use screen protectors and don't leave it charging the whole night.