I also use the M-Edge Trip Jacket Folio Cover Case for the Kindle Touch on my KF. I like it. It was very, very, cheap at the local office supply store (less than half the price on Amazon, before shipping). It's sturdy, simple, and has been through a lot and is still holding well.
Also, yes, it looks like it may not hold well because of the bottom corner pieces, but I've had it for about 5 months now and it hasn't come out unless I have purposely taken it out. I do recommend bringing your KF with you to the store though so you can make sure it is what you want. It's great for people like me on a tight budget.
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