We have our window cleaning business on the flat rate scheme (11%) However it's based on total turnover, you can't deduct anything you buy from it.
It's beneficial for businesses that don't have a lot of vatable expenses, such as window cleaning where you main cost is wages which isn't vat rated. Our other big costs are the vehicles and fuel, but the 9% saving far offsets not being able to claim van on these.
As for a 2 man band not being able to reach the vat limit is nonsense, our normal performance targets are £200/man/day and they regularly do a lot more than that.