It might be slightly less accurate, but is more than enough to handle all background radiation levels. You do not even need to calibrate it, and it is capable of detecting gamma radiation accurately above 120keV within +/- 10% accuracy. How do you use it anyways? Well, you attach it to an iPhone or iPod touch using the dock connection, while the radTEST app will do all the data processing and result charts, allowing you to share the readings on Facebook, Twitter and Google Maps.
Interesting devices, these, and they will definitely be useful only if you happen to live near a nuclear facility or are going to visit countries with plenty of nuclear power plants. Otherwise, if you happen to reside in a countryside and one of these start ticking like mad, either a UFO has passed by in the night and experimented on your flock of sheep, or your neighbor is actually Bruce Banner in disguise.