lure retriever?

[Bladerunner]

i think thats what they are called, correct me if im wrong.. seen it on a fishing show a week or so ago, you slide this contraption down your line and it will knock your lure free if it's hung up or snagged on something..have any of you guys used them? are they worth the investment? (i cant see them being that expensive ,really) the one thing i see happening though is if you slide it down and it doesnt knock it free then you lost the retriever too when you end up having to cut the line anyways..right? anyways, i was just wondering about it, cause i lost one of my favourite lures cause it got hooked up on a log :'(