So let me see if I have this straight, your agreement assigns the IP rights from the get-go, but you don't actually deliver the IP until each milestone is paid?
Seems so simple that it seems to good to be true.
Essentially yes. Any smart employer will make sure that 'whatever you do belongs to us' from a contractual perspective. That's going to be important to them, and it's common. I wouldn't even suggest otherwise.
But usually I send in an invoice as the first milestone is done (usually there is enough conversation/back-forth for them to know the milestone effectively done - or like a web-demo or something), and softly hint that I'll send in the deliverable (i.e. code and assets) when it's paid.
There's no way a company can take you to task for code what you have written, wherein you have not been paid. Even if they did - it would be a long, expensive process and would be a huge distraction from whatever it is they are trying to do. The pragmatic reality of 'you get the milestone for payment' trumps any kind of legal contextually - if they want to move forward they need to pay, it speaks right to the operational reality of their bottom line.
