Junkemailfilter is a web based mail filter similar to how we do our website messaging and positioning. They also run an RBL service and are a well entrenched player. They claim to match the price and are transparent about their schemes and are competitively priced.
Their website looks more drab and less corporate friendly. Not sure about the support levels and such. Overall you get a feeling they are not very open about how they do the job though they make an effort to explain on their website. At least they are not business guys that much is clear. But they do not seem to offer a free trial appliance download like we do. They are operating a network level appliance exactly like us.
They are also OS or email server agnostic like us.