Well I seems I was wrong too!! I purchased the 18X as it seemed to be the newer device. I am about to buy the 40X2 and a smaller one so, an 18M or a 20X...
Two things to note about the 20X2:
- no external resonator capability - might be important if doing time sensitive stuff (like serial comms)
- no external reset capability
..unlike say the 28X2/40X2