A black box appliance might be better in some cases than one where you can shoot yourself in the foot if you configure the drives incorrectly.
All I can say is the last couple of projects I have been on related to configuring and installing SQL could have been solved by just clicking the Buy button on this. However, if you need 128GB of RAM instead of the default 96, or a special PCI card for your SAN you're out of luck. It's not expandable.
The pros and cons and performance of the MS HP Business Decision Appliance from one reviewer.