I do not buy that it is dangerous. However, I haven't seen any statistics showing the frequency of mutacin-1140 or its efficiency. Back in 2015 when I was a teen I did an experiment using colicin V (an E.coli one - I was planning on engineering E.coli Nissile to replace my current gut E.coli with something more fun. Got kicked out of the science fair for that one - https://keonigandall.com/posts/colicins.html ). Turns out, you need a sizable portion of the population to get takeover. I haven't seen ANY data on the population percentage necessary for takeover with this strain. Nor have I seen statistics of its natural occurrence percentage.
I wanted to modify the strain to have GFP expression, so I can have my own little engineered biome for myself that is showable at parties and such, but it looks like they removed comE :( will have to start from an original strain instead, I guess.