I did an open water swim across a lake, 419m there and it recorded 418m return, my friend with a Fenix 5 who swam alongside me had zig zaggy tracking.
The 945 performed perfectly. This was using the beta GPS 2.42 with GPS and Glonass
I did my first ow swim with my new 945 today. Fw 2.50, GPS 2.30, GPS+Glonass. Distance was perfect compared with phone in safety boy. See the two different tracs below, perfect in line! Very happy. 

Well unfortunately I did 3 more swims, only 1 worked the other 2 were totally inaccurate. I swam for 10mins and it showed 115m. So disappointed 2 good tracks, 2 bad tracks so far. My 920XT was not perfect…
1000 is pretty small sample set. Of course collecting it all by yourself is hard, but that was the point.
We don't know at which percentage these OWS fails. Having that data would help.
My first was OWS was pretty ok too, one spike to land, but not total failure, but then I've seen the fails, even with the beta GPS firmware.
Since I've had beta GPS 2.42 (GPS and GLONASS), I've managed to record all my swims, but I not convinced that they are accurate. 2 laps of my local lake last night gives very different results and pace to that that I would expect (and had with my previous 920)