The page says "open source", but I don't see links to the source anywhere so I can see what filters installing this would add. I'm sure it's fine, but I wouldn't add a set of email filters without knowing what they were first.
In my field (bio) it's fairly common not to publish code, but it's becoming more common. Biologist's code is generally crappy and I think everyone understands that. The better developers are often valued for producing tools that are reliable and people can use and get lots of attention and citations for their tool papers.
The mathematicians and computer scientists I've worked with generally wrote more complicated code, but from a bugginess and maintainability standpoint I'm not sure it was any better. I had a mentor with an applied math degree who was extremely fond of one and two character variable names.
Just publish it. Unless your paper is a _BIG_DEAL_ barely anybody is going to look at it, and some people (hopefully the right people) will respect you for showing your work. I think I'm one of the few reviewers that actually try to run and maybe glance at the code for papers I review. In the papers I've reviewed I've never seen a comment that indicated any of the other reviewers even looked at it.
