Andrew ... I did contact the developer and let them know about VoipBl, but they never asked why it was important.
Adding a firewall is a good thing ... but my testing showed it fell down in real world testing and might just give an illusion of security (although everything helps).
There is a great danger that small users will assume that because they have the firewall module they are safe without:
Good logging (and looking at your logs occasionally)
Good password policies
Call logs
Call charge limits
etc etc.
I would hope that the firewall module as it develops could include a link to a best practice document about how to secure your system, and remind users that it is just part of a larger picture.