Basic sensors that you are using for logging and alarm are ok. However, when starting with power/switch/dimm, then security starting to be a big issue. (Also when using the sensors to control something)
I hope this boards will be sold with a big warning on that point.
(I'm not negative to mysensors and using those myself, why would I else be here :). I'm just not a fan of people seeing this as a complete HA solution)

You must set the right baudrate in serial window, otherwise you will only get garbage.
(default 115200)

100% security is probably to hard for arduino (especially on those 3.3V units). So this type of sensors and actuators should not be used for any critical applications. (Do NOT control your stove).
However, there is still use for something between 0 and 100% security, especially to create subnets that don't have the possibility to affect each other.