I appreciate this post was asking about Dexcom One and your answer presumably meant Dex One. For completeness (or accuracy) Dexcom G7 does communicate to my Samsung watch through my android phone. I've never used anything "i" so I don't know how this works with apple products.
Also my android phone is not waterproof and my scuba experiences have taught me that so-called waterproof bags or boxes (eg for cameras) tend to fail unless you spend a great deal of money and have a lot of preparation and maintenance time to spare - which I think might be prohibitive for swimming.
The lost functionality with Dexcom One was, as I remember, in absolutely no event logging capability and none of the tables or reports that Libre 2 generate within the Libre 2 app. You can get some analysis from the web based Clarity "app" ( technically its probably a link rather than an app); but I found Clarity very slow to get going and I only got pdf reports that answered only pre-set queries. The more queries asked the longer it took to get answers.
On Dexcom G7 I can't take a screenshot; it's a deliberate security constraint by Dexcom for G7; [WHY - for goodness sake??? Since the limited daily reports from the app only allow you to see the last 24 hours and not a minute more, in order to compare an event yesterday with today you have to go to the tedious Clarity link just to briefly look back!] So I guess that prevention of screenshots will be so for Dexcom One as well; I didn't try.
I did not like the 2 part hardware for Dexcom One. You get a 10 day sensor but have to clip a 90 day transmitter on top and then move that from sensor to sensor 9 times.
Overall I found Dexcom One constraining and stressful. BUT my body was more compatible with Dexcom One than it was with Libre 2 and since I had a 50% failure rate with Libre 2, Dexcom One was at least more reliable than Libre 2.
