I bought an X4 back in November, and bought an X3 in March, after realizing the X4 was too big to fit on the back of a regular iPhone.

I absolutely love this thing. It's great because of its limited scope and featureset. It just sticks to the back of my phone, ready for whenever, and the battery is good enough that I don't have to worry too much about the dumb connector. I bought a USB C to pogo adapter that seems to work fine for charging it, and keep that in my travel pack.