These were taken at exactly the same spot using iOS 12
I am not sure Three will give the whole capicity of the network, so speeds will be slower than what you get direct with Three.
I'm with iD and have never had much of a problem tbh, but if you are with ee already and can get comparable for only a couple of pound extra a month I would be inclined to stick with ee. Nothing wrong with iD (from my experiences anyway, I'm sure others may have horror stories as they always do) but ee coverage is probably one of the best around.
Anyone know what their 4G coverage is like (uses the Three network). This looks a good deal but I'm a bit put off by a couple of vague statements on their website... We also provide advanced 3G coverage to 98% of the population, so you get the fastest 3G speeds in the UK. And things will get even faster, as the 4G network we use should reach even more of the population by the end of the year. and 4G rollout. We're working hard to increase our 4G coverage. I'm with EE currently and up for renewal and their comparable offer is £15 a month, but their 4G is pretty good, so it may not be worth the risk changing (from my personal point of view).