I work at ZAGG. Now that we have that out of the way, here's my two cents on this topic. There are essentially, 3 types of devices intentended to improve your iPad experience. I will simply state my observations as factually as possible and leave out any opinions as it is impossible to be objective when you work for one of the companies being discussed. The three types of devices are:
1. Leather (Pleather) Folios- Brookstone and Kensington $99
2. Netbook designs- Clamcase and Crux 360 $99-149
3. ZAGGmate- $99
These two faux-leather cases have rubber keyboards missing a shift key on right. The reviews of those keyboards can be found on many sites because these cases have been around for a while. There is a picture on ZAGGmate.com to give you a size comparison.
The netbook replacements like Clamcase and Crux 360 haven't been released yet so it's impossible to know what others think yet. However, their keyboards look like plastic with scissors (generally preferred over silicone but again, I'll leave my opinion about these things out of the discussion). The weight of the Clamcase is 1.7 lbs or 27.2 oz. and 1 inch thick. It looks to be attractive plastic covering the whole iPad. Crux 360 appears to be very similar although pricing still shows $149. I'm sure that will come down. These two designs are made to replicate the look and feel of a netbook. They appear to be ready to ship "soon."
The ZAGGmate is different from the other designs. It is bead-blasted, anodized aluminum like the iPad. It weighs 12.8 oz (less than half the netbook styles) and is 1/2 inch thick. Adds 1/4 to iPad because iPad nests inside. Covers iPad glass but not back. Leaves iPad back exposed. As many have said, it looks like an Apple netbook when closed. If you are concerned about your MacBook being scratched, then you would want to treat the ZAGGmate iPad combo similarly. Invisibleshields, skins, leatherskins, bags, are all very popular for these types of individuals. If you are content leaving your MacBook uncovered, then no worries. You already know about the durability of aluminum. Thousands of ZAGGmates have already been sold and shipped and you can find dozens of hands-on reviews online. You may also want to test it for yourself at your local Best Buy. The ZAGGmate was not designed to replicate a netbook. Think of it as an aluminum case that protects the iPad screen while adding the functionality of a Blutooth keyboard (with plastic keys and scissor action) and an integrated stand that allows for portrait AND landscape mode. We wanted to create a device that allowed the iPad to be much more usefull while also allowing instant separation for the times when you just want to hold the iPad and not have some case or other mechanism hanging on.
So, how do you decide? I think it comes back to personal tastes. They have distinctively different looks and materials. The look and feel is certainly for you to decide. If size and weight is a consideration, the ZAGGmate weighs less than half as much as the netbook replacements and is half as thick. It is also significantly lighter than the pleather cases and also half as thick. If a netbook look is what you want, you'd choose the Clamcase or Crux 360. If you prefer pleather cases and silicone keyboards, you'd choose the Brookstone or Kensington devices.
I hope this helps you make the best decision for you. No matter how you look at it, having choices is always a good thing.