I got a 15inch one for one week and then I returned it because I think the space grey looks tacky. And now I ordered a silver one haha the return it's not 30 days but I think about 14.
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Not a developer, can't say much bout how much the function key is going to matter but i believe if you use it long enough, you can touch type on it like how I could on an iphone.. just a little after a week i can already adjust brightness and volume without looking at it.
About the keyboard, its controversial, but it's by far the fastest and best keyboard I can type on. And i love the short travel.... it makes me type faster in one sense with lesser effort. My speed considerably improved to 86wpm lolol from 80 on the older MacBook pro