I have SLS do a spring cleanup, maintain the lawn and a fall cleanup.
Their work is excellent, and I have kept them for 10 years.
As far as doing other projects, I would be sure to find whether they have crews that do it or they would contract it out. If it is their crews, then I would not hesitate.
The most important thing is to be very clear with your requirements (e.g. removing the leaves or blowing them into the woods) so they can meet expectations. Do not be afraid to be very detailed.
They are expensive, but worth it.