The Iron top scorer moves to the Hive on a deal until the end of next season.
The Bees have won the race and they say other National League clubs and even EFL sides were keen to offer him terms.
The former Staines Town man was on a non-contract arrangement at Cressing Road which means the 25-year-old arrives on a free transfer.
Manager John Still told the club’s website that Bettamer has plenty to offer.
"I've known Mo for quite some time, he was on our hit list at my former club when we were looking to bring people in,” said Still.
"Then I came here and when the opportunity came, we made an enquiry, went through the right procedure and found a way to bring him here, and we're delighted."