We do con roofs and gutters in all weathers, however I normally wait until we have enough to last a full day, on average it's probably 1-2 days a month that we do this.
It's all done with ladders, which I still think is the most effective and best way, some of the jobs today had small trees and lawns growing in their gutters with roots that went half way down the drainpipes and I don't think the gutter vac could handle that!!
I've looked at the gutter vacs, but more often than not we can have the job done with ladders and drain rods before we'd have had time to get the gutter vac out and set up, plus the expense of the machinery is too high to justify for the amount of work we get from cleaning gutters.
We always do it in pairs and use ladder stand-offs and rojak ladder stops.
Gutter/Fascia cleaning and Conservatory cleaning is more lucrative than window cleaning but often a lot harder work.