if you can get an 850 for half the price of a 900, then go for it

They both retail for the same price or very close I think. The 900 offers some programming advantages. If variables become real on the mx900 and I think they will, it is a much better remote IMO. Either way, they are both great remotes. The 850 feels very nice in my hand as well, big plus for me.

850 connects with serial port, 900 and rest of urc remotes are USB

As far as RF goes, as long as you get a narrowband 850, RF is the same on these remotes, check narrow band info at top of page

URC's can be made to work just like harmony's if you have variable and still very similar without (use on button instead of activities turning on, or deal with longer delays).