I made the mistake of buying one of these (The 30" model), and while it really helped me pick up 800 MHz trunked stuff well, it was worse than the telescopic antenna that came with my Pro-2052 for everything else except the National Weather Service frequencies. I ended up breaking down and buying one of
these at my local RadioShack and setting it up in my window sill. I've been very happy with it so far.
On the bright side, the slinkyantennas guy is the reason I found this site. It's kind of funny when I think about it, because very few people here have said anything positive about his wares, and yet he still has a link to RR on his About The Seller Page.
I guess like anything else related to radios, it's all in what you want to listen to, and how much you're willing to compromise (Or how much sneaking you have to do to fly under the radar of the local housing authorities, spouses, or codes departments).