From a point of view of a non-pro dev, hourly invoicing makes me, as a customer, think "we can do it in 10h, but will take 15h to charge me more!".
Even if the project at hand is not your cup of tea, and it will mean learning something new along the way, the customer must not be charged for that learning time. Plus, it will allow you to more easily take on similar projects.
As a customer, I would be more confortable with a fixed quote, even if it meant being over priced, than an hour fee that makes pricing uncertain.