In his blog post on the matter he explains the thinking behind the move. I am interested to see how this will work out revenue-wise for him. Given his figures that only 3% of users pay the patronage fee (which is now a 9.99$/year premium subscription), he can double his money if the ads for the remaining 97% of users will bring in only 31 cents / user / year - this seems achievable to me.

A short look in the app shows me that he went with Google / AdMob for the ads (are there any others after the demise of iAd?). I’m not a big fan of ads in apps. However, I have to admit that I am also not a big fan of subscriptions - what is great about subscriptions for publishers (recurring revenue that keeps piling on and on) is awful for consumers (recurring expenses that quickly add up and require strict budgeting in order not to get out of control).

He rules out the third option - a one-off payment for the app - based on past experience of declining revenues. As a compromise, I would prefer how it was in the old times: You paid one-off for a software package and could use it for as long as you liked, but if you wanted new features you needed to pay for an upgrade. However, the App Store requires so many hoops to jump through for upgrade pricing that this model seems to disappear. A pity. (Okay, I do admit that there are other reasons for this development as well - one being that going without upgrades is a bad idea for many applications these days as any unpatched security flaws will get exploited in no time.)