One place where gutter vacuums are hopeless is where there is some kind of mesh, plastic usually, over the gutter. Presumeably designed to keep out large leaves.
However it also lets in small seeds and these wait until you have cleared the crap out with your vacuum and then sprout - about now with the sunshine.
I have just had to refund £100 on account of this (felt morally obliged to) as her gutters have a nice array of plants growing in them.
So be warned, gutter vacs don't work with mesh in the way.