Here's the Sony Pocket 300 Case Logic cover with my Libre nestled snuggly inside
The only button covered is the '0' at the upper right. You can still press it through the elastic corner strap so it's no biggie. The power button on the bottom of the reader is accessible but the usb/sd card isn't. I'll have to take the reader out of the cover to charge it. Here's the Libre's original sleeve next to the case logic cover for size comparison:
I'm happy with it, especially for the price. I wanted something more protective than the sleeve for my Libre. With it's hard cover and raised bumpers all around the reader this fits the bill.