In the first instance the EM0480 will provide a reasonable job on fresh beans to suit the EM6910... I agree be careful as to the EM6900.
As per many other things... Second-hand goods have pros and cons. If your budget is as tight as I am reading into you post; then try to get a hand on test and ask lots of questions.
If possible get the Serial # and in addition there should be another 3 digit number stamped into the label ( Open the rear door and look at the label and Bar code - Lower L/H side of the machine.)
This 3 digit is a DOM and will assist in working out just how old the unit is.