I have one and have nothing but good things to say about it since nothing bad has happened. I got it locally for about $120 and liked the fact that it has a warranty and can be mounted anyway I choose.
I never have to worry about my battery going dead and getting stuck on the wrong side of town in my baby....
I usually hit the extremes in Utah. I just bought it at the first of the year, so I don't know about the heat yet. Haven't had a problem in the cold, though. Battery is bigger than the tray, but oh well.
I have a redtop. It works pretty good. I can run my lights longer than i can with a regular battery. Its nice not having to check water in the battery or being able to mount it anywhere. It is too big for the tray though! =/ Need to get some kind of custom hold down for it. I bought mine for 25 bucks from centennial battery distributors. I'm a friend, so i got a good deal
I've had one for about 6 years and get it tested about every 6 months or so. Last time the guy who tested it commented that it tested out as brand new. I say go for it. This one has lasted through three cars and no signs of getting weak.