My business does 6 figure sales running all s2m platform - and has been since 2010. These 3 these statements are true:
(1) it's robust and flexible and well-designed.
(2) The UI is not friendly and it lacks important things like Donovan states - a checkout upsell is a good example.
(3) Despite good support from thankless devs, there are still bugs in some basic, key features. Good luck getting it to integrate with recurring commissions with idev; free trial is very buggy and untested.
I don't complain too much having paid ~$100 for it. BUT my dev costs and bug-fix costs are into 5 figures. I would have rather paid wpsharks for solid add-on features, but they aren't available. For this plugin to go prime-time they (Jason) would need to employ (pay) for QA testing and plan some new features that are important.
Any comments or insight from s2m devs or wpsharks appreciated.