Ariel Michaeli, writing on the appFigures blog:
When it comes to making money, users seem to be fine with paid apps. Unlike the iOS App Store, on the iMessage App Store only 7% of top grossing apps are free(mium). That’s just 13 apps!!!
The remaining 93% of apps (187, to be precise) cost between $0.99 and $4.99, with the majority (61%) having a price of $0.99 and 36% having a price of $1.99. The remaining 4 apps split between the other price tiers.
Monetizing upfront is great for developers because it’s simple and easy to implement, but it’s also a sign of a store that isn’t mature. If the iMessage App Store matures similarly to the iOS App Store—which is likely considering it’s the same audience and device—we’ll see a strong shift towards freemium. For now, developers should make the most out of it.
Speaking from personal experience, the iMessage App Store's top charts are a constant source of discovery for new paid sticker packs from indie artists. These first numbers from September seem to be holding up so far.