I agree it's nasty. And it's certainly not my style. It's the first time I did this in 16 years. But, what you probably don't know, this little campaign is running at least since September 2013:
Remove the animal to make the link work: http://<kangaroo>www.gpsoft.com.au/dscripts/compupgrade.asp
Tit for tat, as they say.
Don, and I say this criticism as constructively as I can, the difference between what they did on their web site and what you did in your post is that they had a firm, concrete list of advantages of what their product could do over the products they were advertising upgrades from. If you had approached your sales pitch from that direction I don't think nearly as many people would have had a problem with it.
Compose a solid list of what your file manager can do that others cannot and use that to sell your product. Advertise by building yourself up, not by tearing others down and you'll run a much more successful campaign, IMHO.
EDITED TO ADD: Offering a competitive upgrade is awesome. It just was not presented as well as it could have been.