I'm really curious to understand the different tips and techniques you use to measure CPA (Cost Per Customer Acquisition) for your startup business.

My business is focused on delivering a set of mobile products to a distinct (almost niche) user base and I'm on a mission to really understand my key metrics, CPA being the first. However as we deliver our solution via a third party (in this case the app store) I feel that we are are at a disadvantage to our SaaS counterparts.

If I look at our customer flow, its a pretty familiar story starting with some lead generation activity (in this case Google ads):

Adwords > Dedicated landing page > Link to App stores > Download / install > Register

Now I can measure everything in detail up to the point the user leaves our ecosystem and ends up at the Apple or Google store. So I am curious, how do you manage this if at all or am I expecting too much?