I have never used the Apple Smart Keyboard before and tried it today at the Apple store with the 10.5 iPad Pro.
1. Do you get used to the keys spacing over time? It was unusual/uncomfortable to type on the keyboard compared to other keyboards that I have used.
2. It is very expensive and I am not sure if it adds any value to something like a $40 JtechBluetoothh keybaord that I use. Your thoughts?
3. The back of the iPad is exposed. Thos of you who use this keyboard, how do you protect the back of the iPad?
You certainly adapt to the keyboard - give it a day or two and you'll be as fast as you are elsewhere. I believe it's the same size as a full size MacBook keyboard but the actual button area is smaller with larger gaps. If you were to imagine the keys being wider, the same muscle memory should start to kick in as the positioning is quite similar.
I personally don't like the cheap ones - you can really tell how bulky the case is and cheap feeling the keys are on the inexpensive ones. That's fine for some, but it's preference. I think the Apple keyboard feels nice enough to pound out long work without issues, and it doesn't require a Bluetooth connection, separate battery, or separate device to charge.
As for the back of the iPad - I don't think it's necessary to protect that while you're using it. I recommend a sleeve to store the iPad + keyboard in while it's not being used, but there isn't many situations where you're going to accidentally damage the iPad while it's docked in the keyboard and being used. Apple's sleeve (the one with the Pencil slot) is really awesome and fits the iPad+keyboard combo *just* barely. Unfortunately, it's another $129 which is a bit ridiculous, so I'd go for some sort of Incase neoprene sleeve.
I really don't think it's necessary to cover the entire iPad in some sort of always-on case, unless you're taking it hiking or something like that.