Personally, I wouldn't turn up with a powerful gutter vac and not be using a genny.
Gutter vac'ing is like any other sector, buy cheap, buy small and you won't be able to do the job properly.
We have an omni vac and it's been good as gold for 5 years, however there prices are way, way over the top.
Numatic have a very good wet/dry vac which will blow and suck for a decent price and you can go direct to the carbon pole manufacturer and get poles for 1/3 of what omni vac charge.
There's not a lot to putting the bits together for a much better price than going to a company that quite honestly will flog you an underpowered vac which seems a good deal at the time, or paying through the nose for a decent vac and poles
Darran