Good point - I have pushed the lens into branches, flower parts, etc., and definitely recommend a UV filter. I have a B+W MRC UV on there (as on all my lenses). However, the filter prevents you from mounting the MT-24EX to the groove on the front of the lens. My solution is to screw a Macrolite Adapter 58C onto the front threads of the filter.
Interesting on the filter. I was able to put the MT 24EX on the MP-E 65 and then screw the UV on the macro lite. I wound up getting the 58C but don't know if there is a need a this point. Anyone have any ideas how else I can use the 58C when the UV screws on to the lens or the flash after its on the lens. Don't get its purpose (the 58C)