There isnt really a banrate since there are many factors that lead to bans and the script only being a part of.
This script is running flawless (on mirrormode too), supports pretty much every location so you can choose areas with less players and also killing crabs is obviously a rather low interaction activity so overall bans are on the lower end of the spectrum when it comes to the script.
Check out the first post in this topic, there are bunch of screenshots of people running for many hours at a time (with breaks) with great success.