Easy to make, worked first time. Seems accurate enough when tested with my radiation sources.
Battery powered, so it can be used as a portable device, unlike many other kits. It also has the satisfying Geiger counter `clicks` so you can hear the radiation level.
USB communications via plug-in FTDI TTL-232R-3V3 cable, or via Arduino (etc) RX input.
Digital pulse output can connect to Arduino (etc) input so you can write your own code to smooth and convert counts to Sieverts.
One small point: You need a 1 giga-ohm resistor for accurate HT voltage measurement. This could have been supplied with the kit. But it works well even without adjustment.