Just a quicky on my limited experience running Rpi 3B with a wittyPi hat in bt and wifi (no cellular).
Downloading software and getting it running is pretty easy and the manual is good.
One thing that caught me out, in the scheduling .txt files, the start and end times need some thought to your application.
For example Influx takes a while to start so if you want to be able to SSH to your Rpi on the hour (say) its better to start a few minutes before the hour etc.
Mine is set to ON at 56 mins and OFF at 20mins at the moment.
Also (obviously to me now) the Rpi needs to be set to boot without a password.
Not sure how this stands security-wise.
Lastly, running a few tags and with HDMI and mouse/keyboard plugged in, 20min ON per hour takes exactly 100mAh, without the peripherals and set to boot without GUI it pulls 80mAh.
Just got to get it working with cellular now.