All I know is that while there haven't been program updates in a while, the database updates seem to keep coming. And the couple of times I've sent a problem report about a site not displaying well because of Ad Muncher, the next database update fixed the issue.
The big things that I've heard mentioned as problems are HTTP gzip support, HTTPS filtering and IE11 support. These aren't problems for me, but anyone considering a purchase should be aware of those things in case they might be important to them. The software works very well for me, regardless of the state of the support for those things (when I surf on a machine without it installed, it's painful).
Ad Muncher isn't cheap - in my opinion, the 50% off deal is what makes the price bearable, particularly if you're going for multiple licenses. I also opted for the Basic option, which helps with the price, but only gets weekly list updates instead of daily list updates. I think that's the only notable difference between Basic and Premium. There may be other software that works as well or better or cheaper (or some combination), but I haven't been driven to look for an alternative so I don't know if that's the case or not.
Finally, I don't think there's any problem with clarity of the lifetime license. The purchase page says (emphasis added):
How long would you like to receive new program and list updates?
With a popup link explaining the "Unlimited updates" option:
Feature Details: Unlimited Updates
Unlimited updates means you get program and list updates indefinitely. No further purchase will ever be required, and you will be saved the trouble of renewing your license each year.
Ad Muncher has been continually updated since 1999 and isn't going away any time soon, so this is a worthwhile investment to ensure you continue to receive the best browsing experience possible.