Been on dexcom for 3 months now. I have not had to send any back, all lasted full 10 days.The dexcom app isn't more basic, just different - you can get a lot more reports, and look at your graphs over 1 hr, 3 hrs, 6 hrs, 12 hrs, 24 hrs, though you can't type in notes. I use the modded version (build your own dexcom app) which is the offical version minus the code that checks if its 'on the list' put together by some rando on reddit.
You get the full 'stapler' everytime and in my experience you are less likely to get a 'stinger' with dexcom. Its officailly approved for tummy as well as back of arms, both work well for me. Application isn't quite as straight forward as libre as you have the bit that sticks on you that lasts 10 days, an a transmitter that lasts 3 months but its no so much of a faff...in an emergency you can restart it and you can get another 4-5 days easily with a good accuracy.
The dexcom is more acurate for me, and more accurate in trials, and can be calibrated, though if you need to do this its mormally just yhe once. I tend to rely on it to treat lows, and they say you can do that, unlike with libre where you need to check. For me, it gives very few false nightime lows compare to libre, wjich was the reason i wanted it. You can set a different set of alarms for night (i set my low alarm lower overnight as things move slower without a bolus insulin being active). In general, there is a LOT more flexibility over alarms, which i like, and you can change the sounds so you know what the alert is for.
Not sure re shower but fine in bath. I find bs go up in bath, but i think thats me, not dexcom.
I always use an overpatch so can't comment on adhesive, i think its less limpit like than libre 2, but i've not lost one yet.
It does, however, resemble a wee coffin (sad face emoji)