I just checked out some screenshots and it sounds like a great buy. What's the maximum strength you can set it to? My guess is that it probably hovers around 2200, which is more than enough for some quick playing.
I have Shredder 9 for the Mac (they're in v12 right now) and it's fine. It gives += type of evaluation with some numeric values and is a good analysis tool. For Windows I use Rybka 3 and Fritz 11 (v12 just came out). I like Fritz because of its commenting when you set it to run a full analysis of a game. I wish I could add some to the program like "What a patzer move!" or "You don't understand this position, do you?".
I find Fritz very easy to use, but Rybka can be a bit confusing. I still have to spend more time learning to use all its features. It's a bit like PhotoShop: you can do some great stuff with the program, but you need to learn how to use it.