I am (personally) alright with this model. $150 is on par with OmniFocus Pro [0] which I've gotten easily more than $150 of value out of. (Including prior purchases of earlier versions, and similar price points.)
With todo apps, I don't really expect the same sort of constant on-slaught of features like I do from other things. I expect it to continue to work and get out of the way. I expect the price to reflect the fact there was a lot of upfront work to get it "done" to a level where I can just use it.