It's not a bad idea, but this implementation seems overly aggressive due to the follow-back rule:
> Additionally accounts following more than 200 other accounts, but also has less than a 1% follow back count. (IE 200:2, 1000:10)
That's not a difficult criteria to fail, especially not for a new'ish/read-only accounts, doubly so if you use starter packs (themed collections of users that you can follow with the click of a button). I could see a number of obvious false positives just from glancing at the live feed of blocked accounts. Such as the newly created account for the Brussels School of Governance [1] that is following researchers from that institution. Another example was a named author following a number of other authors and writing/publishing related accounts.
EDIT: Part of the problem seems to be that accounts are evaluated (and added to the list) mere minutes after they are created, before anyone has a chance to follow them back. That could be mitigated by delaying this check for a few days or so.