I can only talk to Panasonic (GX8) and Fujifilm (X100F, XE3), but for both of those it's still pretty awful. Transfers are very slow, especially if you want full resolution, and it's always frustrating to just connect my phone to the camera--the apps are slow and clunky, setting up the adhoc network is flaky, and often times even after connecting it'll suddenly just disconnect for no reason. The XE3 supposedly supports a persistent, bluetooth connection that'll auto connect and auto transfer photos, but every time I've tried to set that up, it sends like the first two photos along and then doesn't work anymore.

I've moved to just using an SD card reader.