The protectors fit fine on our Split-King: however we are still getting used to the extra material and feel under the sheets. It's a minor difference but noticeable.
The protective cover is a no brainer why not buy that to protect your investment haven’t spilled anything yet or any per accidents but you never know its peace of mind with it buy it
I'm not a huge fan. It doesn't grip to the bed too well, it's very thin and not at all soft or cushy. It doesn't make a ton of noise, but it's slick in a displeasing way. Maybe there's a reason it is the way it is but I would prefer something thicker and less like a plastic sheet.