I had thought about one of these units, but keyboards are a highly personal item, and unless I can "test drive" it in the store, I'm usually reluctant to order a keyboard.
That being said, I did have the Microsoft Wedge mobile keyboard with my SP2 previously, and I liked it quite a bit. With the move to my SP3, however, I did find it a bit cramped compared to the Type Cover for my SP3 (though the flimsiness of the Type Cover is still it's biggest downside).
So I went a completely different route....I ordered the Lenovo Thinkpad Bluetooth keyboard with Trackpoint instead. I've never been the biggest fan of touchpads (though admittedly Apple has done a good job on this point), and I was always a fan of the Trackpoint instead. Compared to the Wedge Mobile keyboard, it's slimmer, albeit taller due to greater key spacing and a small palm rest at the bottom. It has that classic laptop keyboard feel (not as good as the old mechanical switch Thinkpad keyboards from 10 years ago....but overall, pretty good), while still being ultra portable.
Now I just take my SP3 everywhere I go, and can leave my Apple rMBP at home. I still use my Type Cover mostly as protection for the screen whenever the SP3 is in my laptop bag, but take it off as soon as I setup in my office / home / customer site.
I suppose I shouldn't be so paranoid about protecting the screen, but I can't help it. Now I just need to find a super slim case that also allows me to still utilize the kickstand (The Incipio Feather still looks too bulky for my tastes).
Okay, slightly off topic, I guess.
Patrick