Summary of contributions for reference letters
There is no reason, actually, not to do both. What you suggest is very likely a good thing and will save the writers a bit of time. But you can have a bullet pointed introduction followed by a longer description of the work. Make sure the second part is labelled as such. If the prof's memory is jogged by the first part they have no need to keep reading. Otherwise they may appreciate it. 

You could even use wording that they might want to copy into a recommending letter. Make their life easy.