@Dave44 - Don’t want to rub any salt, but to address this part of your post. On the app, there is a setting to change the scale from 400 to 300. (I think - app not actually in front of me - hope I didn’t get that wrong!!!)
Also, Dexcom Technical Support has told me that the more simultaneous devices you have paired with the G5 transmitter, the faster the battery in the transmitter will run down. Dexcom provides a warranty on the transmitter for 3 months intended for 2 devices if the transmitter is first used within six months of the SB date on the box. (Again from memory - if wrong - please correct me.) Both the Dexcom App and the Dexcom Receiver (and presumably the X2) have a software switch which will disable use of the transmitter after about 3 months and 3 weeks since it was first activated. So, using 1 device or 2 devices with either the Dexcom App, Dexcom Receiver or Tandem X2 will not practically matter as the Transmitter should still last 3 months and 3 weeks.
xdrip bypasses the software switch so that is entirely different.