I bought one of the ispindel kits (~£50 posted), and have been really happy with it.
There was a mistake in the instructions which led to me frying the charger circuit, but they replaced the parts for me FoC.
Building was pretty straightforward if you know how to solder (I haven’t done it for years, but it was still ok. The temp probe is a bit fiddly as the pads on the pcb are very close together, but otherwise it was fine).
The hardest bit for me was flashing the arduino, as I only have a Mac, but I worked it out after a couple of evenings reading articles about using python in command line. I believe the pc process is much more straight forward.
Calibration worked first time no problem for me, I just needed to gaffa take a couple of bolts to the chassis for ballast.
After that put your WiFi password in and it looks after itself. Ubidots seems to work pretty well too and can be accessed from anywhere which is handy.
Only regret is buying the smaller battery as it does need recharging every couple of uses.