Not every device allows to record both sides. Root is often needed. For many people it's just easier to buy the app rather than read the description. Then complain that the app doesn't work as they want. If the price would be lower, there will be much more such people who buy the app without reading the description.
If manufacturers would implement call recording on their devices as described in the Android
documentation, then the app worked on all devices. But they don't. So I've to purchase many different phones to provide support for them. For example, a week ago I purchased Samsung SM-G906S to add support for Qualcomm 805 based devices, because without the device it's not possible as there are no documentation or required source code. Even with a device it's often not possible. On some devices the system provides
distorted sound, people blame the app, but it's manufacturer's fault. If it was possible to fix, I'd fixed it.
So the app is for people who understand why they need it. Trial version is always available. It's stated in the description, but I have to answer on many emails from people who didn't read the description, but would try a trial version. Why they can't just read the description? I don't understand.
The license attaches to a gmail account, so it's possible to use the app for years on a different phones. I don't think the price is high when you are using something for years and it's useful to you.
P.S. It is the cheapest app for call recording on the Play Store with a rating 4.5 or higher at the moment.
Advertising in the app for rooted devices?
Heh.