There are two primary benefits from having all of your transactions and revenue come from the app store.
The first benefit is the one you have already decided was the most valuable when starting the execution of your app: the distribution channel. There is no easier way to reach your users' smartphones than the app stores already installed on their device. When you get into the Top 10 and Top 100 list of your app category, you will experience surges of downloads and revenues.
The second benefit is the one that isn't spoken of much anymore as the world has acclimated to the technology, but it deserves mentioning: one-tap purchases. Prior to this technology in both app stores, businesses had to work with credit card processors and merchant services, and integrate all of them. Today, there are multiple platforms that make this easier, but it is still what Twin Engine Labs considers "plumbing" costs: ie. writing integration code to solve problems with known solutions. A certain amount of this has to happen, but the vast majority of that code is abstracted away when you introduce the features the app store brought us.
If you are unable to offer digital goods or services to the users of your app, you will unfortunately have to fight the good fight of merchant services integration. But for the rest of the readers, creating integration with both app stores is fairly straight forward, and allows your users to simply tap to buy. No more credit card entry. This will always result in higher conversions because it enables the user to make a decision quickly and act on it simply.
There is, of course, a cost of doing business within these mobile distribution channels. First, both app stores take a30% cut of all revenues that flow through your app. That means if you are charging $0.99 for an IAP, then you will actually be receiving $0.69 for the conversion.
Finally, there are the additional, often hidden costs of marketing your app via cost per install mechanisms and PR.
At Twin Engine Labs, it is our opinion that this is a reasonable cost considering the ease the app store provides as well as the distribution channe.