I have a cheap JETech slim fit case from Amazon. It's much thinner and lighter than the official two piece complete case from Apple. The JETech is also VERY sturdy as a stand. It is poor though at keeping the top lap secured to the back cover when flipped open.
I had the Logitech create keyboard and case. It is ridiculously bulky, heavy, expensive, and a lousy keyboard. Not that easy to remove either. For the price of this plus the 12.9 iPad Pro I think the vast majority of people are better off with a laptop. I have owned literally EVERY model of iPad ever made and tried many many cases, keyboards, etc. I finally realized keyboard folios make no sense to me at all. If you want to turn your tablet into a laptop you are probably better off with a laptop.
Two best keyboards I have found
1) Logitech Keys-To-Go for iOS / OS X. Ultra portable, spill proof, quick pairing button makes it easy to to repair with different devices on the fly.
2) Logitech K811 iOS / Mac Keyboard. This one is approximately the same size as Apple's Magic Wireless keyboard, but slightly cheaper and vastly superior. Better typing feel, backlit keys that come on with a hand sensor, and can pair with 3 different devices and switch between them with a touch of a button - no unpairing/repairing required.
The ONLY made for a specific model of iPad Keyboard cases that make any sense to me are keyboards like Logitech's ultra slim keyboard cover. The iPad is secured magnetically in a slot, and in some cases tha angle is adjustable. The iPad literally just lifts out when not in use retaining the benefit of a tablet, and the secure magnetic slot allows it to be used on a lap with the keyboard, which does not work with separate keyboards. Unfortunately, the latest model is for the iPad Air 2, no pro model, and cost cutting on that model makes for terrible quality - and not even a rechargeable battery - have to replace batteries - WFT?
I found the smart connector or also be anything but. It is not secured in any way - it depends entirely on constant contact - such that the slightest wobbles cause disconnects.