I have the 220v Omnivac. I dont really do any building site work and sometimes I have to work inside courtyards. The generator is too far away. Using the 220V version you can just plug in to the clients supply with out the hassle of moving the generator or lugging a transformer.
We have also decided not to use the Omnivac in a cherry picker as it would be very easy to overload it as the machine fills, especially if the gutters are wet. We have found manual clearing quicker as you can leave the water to drain, not remove it. (Some mewps have a 110v power line running up the boom). If you were a skinny person this would not be an issue but I weigh about 16 stone!!!
Hope that helps