I have had a Polar S725x for two years and used it for training + doing two ironman races. I also have the foot pod for it. I like it a lot and its been very reliable and accurate. Also, they are just bringing out a GPS based pod for it. The main reasons I got it rather than a Garmin system were it’s a lot smaller, has much longer battery life, has great training software and you can swim with it.
It doesn’t autostart and auto stop on the bike though.
As for GPS navigation - well that would be nice gadget to have but in reality I’ve never needed it.
Hope this helps.