We have one. I think it was $250 supplied and installed IIRC, almost 3 years ago. Got it done by Brian White (BriWhi on the forum). We'd originally purchased one at HD for close to $200 plus taxes (i think), but it wasn't as high quality and it was almost $200 plus taxes before installation. So we took it back and had the better one installed for less money overall. Which was nice!
Working great so far, lights still green ... they will go to red to warn you when it's taken a large enough hit or hits that it should be replaced. Been almost 3 years so far and it's still full-on green, knock on wood. You just need to remember to check the lights every now and again; we try to check it after major storms. Here's a pic, it's at the bottom of our panel:
