Once its once it cant be disabled

Update: whatever recent changes were made have caused the app to be unable to be disabled. I suspect this relates to cookies but there must be a way to disable it easily without uninstalling or clearing every cookie.

So Ad Block gets a solid B given that its one of the few apps having the ability to safely block annoying device-wide, and not just the browser. It also works on both wifi and cellular networks.
In my estimated Id say 90%+ of ads are filtered simply by using the default global filters provided by the devs. Ive supplemented those with several of my own because iCab Mobile has the ability to display sites not being blocked and by process of elimination I can usually figure it out.
That being said, the most glaring shortcoming is the inability for users to include wildcards in filters, which makes the app useless on sites that increasingly use random digits before/after a keyword (i.e. 123advertise$) which make wildcards a must so (*advertise*) can be used as a valid block. This will also have the effect of reducing the massive list required to block by domain and prefix.
The developer have an alternate app that has wildcard functionality but it doesnt operate on cellular service. It also has redirect capabilities and more, but IIRC the developers host each users block file via custom URL. My knowledge of networking is limited but my apprehension is based on whether this added functionality could pose a potential security risk.

LAX20531 about AdBlock - block ads on iPhone, v3.0.0