A couple items..
1. a pop account is a protocol, just used to connect to any email account.. It can be a private domain or public like yahoo, gmail.. etc..
2. The app uses private domains for 1 reason.. They actually through testing stick better than using public domain such as gmail, yahoo etc.. Their are more filters to detect public emails domains than private by far.
3. Private domains you typically receive the verification emails much faster allowing the app to create accounts much faster.
4. This was a concern for many users, that is why its best to load up 5-10 private domains, the app then randomly rotates between these throughout the linkwheel account creation process, reducing footprint considerably.
5. With the catchall feature the app is able to auto generate usernames for you, so you don't have to spend time loading in usernames and profiles etc for the app to use, this comes all pre-loaded so you don't have to worry about these details.
Hope this helps.