It is up to you but the RS21 module is currently not supported and adding such support on your end is few months of work, not simple at all.
You can use Xbee wifi and write the drivers in coupe days. The community is already working on generic XBee drivers so maybe you and other can join and make this happen. I know many members of this community will find it very useful.
BTW, I am not adding any more info on top of what been said already in previous posts and what is already explained on the catalog