What's the difference between these and MR? There is no datasheet and not even a pin count available. Yet you can already buy XR from e.g. Mouser with a lower price than MR. Mouser has a datasheet for it, but it is just the MR datasheet without anything about XR. Atmel site only shows the module size, which is clearly smaller, only 7.5 mm x 10.5 mm. According to Mouser description XR with an external antenna and ZR with chip antenna.
Are these just a smaller form factor modules with the same functionality or is there something new or missing?