Following recent public FCC filings for a new Polar, here Polar’s site shows a replaceable strap. Not giving too much away other than ‘it’s round’. Which we already knew.

Last Updated on 18 September 2016 by the5krunner

tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors.

https://pbs.twimg.com/media/CrX3g40UMAAVavs.png I’ll just leave that here.
huh !! not invisible then
I think this will be a sub £100 GPS watch, possibly sub £80 looking at that tiny screen. Note that it’s traditional LCD with custom shapes rather than pixels all over.
Doubt it’ll be sub £100, it looks terribly basic but it does have optical hr. still think they’ll price it £129. Polar and Suunto always launch at the upper end, usually within a month you can get 20-25 off the high rrp, that kind of discount can take 6 months with Garmin.
small screen + optical HR … actually this is what is needed by small-wristed people who find HR straps unpleasant. A surprisingly large market at the entry level. In fact more of a market than the entire triathlon watch market!!