Is is bad to change what type of contact lens you use?

Not usually: I frequently operate under the rule <<"if it aint broke, dont fix it">> so if a patient is happy with their current lenses, change the prescription as needed and use the same one. But there are changes in this field every month, new and sometimes safer designs, and unfortunately the all to often buy out of one line by another firm, simply to get rid of a competitior. You then have no choice.