We had a nanny for the first 2 years; we made sure she had a business, and we paid the business. Essentially, we outsourced to her, rather than another company.
If you are curious about it, use the service for the first year / rest of this year, but follow along as if you are doing it yourself--like an open note test. If you find it too complex to follow, then no harm done, particularly to your nanny. If it's a piece of cake, then switch at your convenience.