this is the easiest and fastest way for who's willing to take that risk
Yes, if they're dry.
Prob is, many times they are not.
They don't have them cleaned for years so the leaves just sit there, they break down & turn into organic matter, it then rains on them & they turn into mud !
Its quite time consuming then, not to mention wet & sometimes smelly.
Also, the gutters may be double story, too steeply pitched to walk on, slate roof tiles (easily breakable), over hanging branches, other obstacles, too narrow to get your hands in, sharp, not enough room to get correct angle on your ladder, etc, etc.
If you're gunna quote on gutters, my advice would be to have a good look in/around them first, too many variables.
ps, if your gunna do it with a blower, battery makes it far easier.