How can you have an accurate estimate when you're multiplying it by 10? A small error in your original estimate gets multiplied by 10. If I'm off by 10 days in the original estimate, that means I'm off by 100 using your method.

Also, I think by definition, a non-trivial project obviously hasn't been done by you many times before. Doing something you've done a dozen times is trivial in this sense.