I can't think of any pro's for a single sided hedge trimmer.
I have an earlier version of the Echo double sided hedge trimmer, it's a very good unit. I bought it about 18 years ago. I only ever use it where space is too tight to use a pole hedge trimmer, so it stays in my shed 99% of the time. But when I do need it, it works well.
My hedge trimmer of choice is the pole type - double sided.
Single-sided trimmers are lighter. You can then put on longer shear blades for wide, long hedges--down one side and up the other without missing a middle strip and requiring a third pass. If you're doing a mansion you probably need a single-side trimmer.
Most hedge trimmers are double-sided, allowing changing directions. These are the most popular, easiest to get parts for, and staple of middle-class hedge maintenance.