The xM1 is a great xSeries implant, but there is currently no stock, and nobody knows when/if it will be back in stock because of chip supply sourcing issues.
HOWEVER
I highly reccomend the FlexM1, I use mine a lot, the performace and read range is really good,so if you are considering getting one, go for it!
If you weren’t aware, you can also store NDEF data sets * with caveat