There are free and premium versions available for each platform. I have purchased the premium version for both the iPad and a Windows PC, but neither for Android. I do not know for sure what additional features the premium one offers. Many people use the free version for their planners.
Metamoji Notes is very similar to GoodNotes in its setup, but there are some notable differences.
While the monthly and section tabs on the planners are functional in GoodNotes, Metamoji Notes does not support that function. However, there is a way to set up the metamoji app so that there is a thumbnail panel of each page visible on the left side of the screen. You can scroll to find the page you want.
It is also possible to create "jump" destinations within a document which can work very much like the links on the tabs.
Another drawback to this app is that you cannot import PDFs to use as stickers on the planner. You must import them as a jpg or png file. If you have a pdf you want to use, the easiest fix is to pull it up and screenshot it, sending it to your camera roll. Then you can import it into Metamoji Notes with no problem. It just takes a little extra time as you will need to do this with each pdf you wish to import. (Note: you can import PDFs as documents).
Syncing does not to be quite as much of an issue as it is in GoodNotes. In fact, having just changed to a new iPad this week, I realized as I was writing this post that i had not downloaded Metamoji for it. I did so and signed in, and immediately my items began to show on the screen. That's service!
As a GoodNotes user, I am not as familiar with this app as I'd like to be. I do know the people who use it really like it. It's pretty cool that it is available for all platforms, which would make it great for use in many situations, including the classroom.
I'm linking the online usage guide here and on the navigation menu for your convenience.
Metamoji Notes Guide