The whole iCloud “omg almost out of space!!” nag screens really irked me on iOS, and doubly so because of their usage of private APIs to both show those nag screens and how the iCloud service works in a way that no other service can, again due to the private APIs they use. I pay for it now begrudgingly because it does “just work”, but I also hate them for it as I’d rather have a choice of cloud storage providers that could automatically back my photos up in the same reliable and integrated way that iCloud does.
I used to use the One Drive app to backup my photos on my iDevices. The biggest pain was the first upload taking forever and it was not automatic. My use case was a secondary back up so it didn’t bother me.