Hi Nikki,
I use the G5. Honestly, I don't think it makes that much difference in terms of battery life (I have an iPhone 6S, and to be honest, the battery life is naff anyway). I don't really know what the difference of G4 vs G5 is, apart from the receiver, although I can say that not having to carry around something extra, as I did with the libre, is definitely one less stress to have to deal with - and one less set of batteries to replace. For me, it has been a big improvement over the libre, but different people have different experiences re the adhesive and accuracy. I like the alarms, although you need to decide for yourself what to set them at - don't be bullied by your HCP into having them set at a level that doesn't work for you.
Hope this helps,
Eleanor