Since the final version isn't out yet, noone can say for sure. From what we know though, if you just want to quickly check something like your emails or a website, ChromeOS will be much faster and easier than using any alternative.
In terms of cons, I doubt it'll be very customisable as most of the time you need to be connected to Google's servers to do anything. This means that the chances of actually downloading and installing new programs/games onto the OS seems quite unlikely.
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