(and now Google Translate returns "geek" for "smanettatore", I don't know if it is correct. "Smanettatore" is a person who puts his hands everywhere, in hw & sw , and I wanted to call you "smanettatore" )
I worked with them some years ago making some prototypes for an automated irrigation system for large extensions (cable was, and is an expensive and hard to maintain solution). Unfortunatelly, the project went nowhere but it was a nice experience.
It was before Digi acquired it. I think the company was Maxstream...
Easy to configure and work with
And with a directional antenna the range can be extended
I'm also a big fan of the ESP8266 . +1 for the January tutorial
However, in my opinion the point for the xbee modules is its range and the fact that the 802.X.X protocol stack allows for mesh configurations. I could reach about 2Km (outdoors) or even more with some hacks. Don't know if max RF power has changed (though I think it depends on the version (Pro) and possibly regulatory differences between countries)
With ESP8266 you will not have problems. 2 years ago I worked with WiFly from SparkFun,which is similar. Next year i start with ESP8266, huh, wee can then compare our results.
It was about 2007/2008. We started the project from zero with some friends and made t work. I abandoned the project and others followed but it never reached the end user. Each node in the prototypes was able to read RFID, sensors, GSM (of course not all of them had it), even send alarms and receive commands through SMSs which then they sent to the remote node. So, you could control everything from your mobile with SMSs while you were taking a coffee at the bar
About legality...I think it was in the limit
Not sure about bandwidth, but I think it's not too much. Also, regulatory issues: on one side max.power, but also on the other side there is a max percentage of time you can keep the channel "busy"