I agree that it's a good product, but I've run into problems with one aspect that makes it so fast - it uses linked servers for compares between different servers. This works great if you use SQL authentication, but I've run into issues with NT authentication because there's no passthrough enabled on most SQL installations. (Feature requires AD to work properly.) This has been acknowledged by Lockwood, but I'm not sure what's been done since I tried the product last.
I do agree that it's very powerful and useful. If the NT authentication piece worked right away, I'd probably be using that instead of our current product (slower, but it connects easily to all servers).