Throughout FollowNFT.sol, regular ERC-721 approvals are not used for access controls. For example, these are the access control checks when follow() is called with a wrapped follow token: 
FollowNFT.sol#L317-L327
Apart from follow approvals, the function only allows the token owner or approved operators (address approved using setApprovalForAll()). If a user is approved by the token owner using approve() he will be unable to call follow() despite having control over the token.
This isnt a major issue as the approved address can sidestep this by doing the following:
However, this could potentially be extremely inconvenient for the approved address.
Consider allowing addresses approved using approve() to call the following functions as well:
