Pros:
- Pricing is fine with me - I'm doing a paid SaaS app with relatively high per-user revenue. You will likely price out most of other devs, however.
- I like the retroactive analysis. The idea of grab everything and let god sort it out speaks to me.
- I like doing both device and web analytics in one place. I don't think doing one or the other makes sense anymore.
Cons:
- I don't see a way to make sure a user from different devices is counted as one user, not two. I want to track the user across all touch points. From experience I know solving this problem is very-very hard - sometimes you want to see what the user did before he identified himself, which is where your idea of "one user per session" falls apart - a session might have different users in it signin in and out, and then there is a period between signins which can be attributed to either of the authenticated users before or after in the same session. Not to mention apps with support for multiple-account apps, (e.g. iOS gmail app where identity depends on which part of the app you're in).
With all that said, I don't think I will be trying it out. There are tons of analytics services out there, and I don't feel like I can make an educated decision about which one to try first, or at all. Where you can help me is by providing a survey of the problem space, talking about the problems, potential solution methods, and then addressing which products implement which methods.
Good luck.