We recently purchased a Scratch Square for our two dogs, and it's a big hit! They're always thrilled when I start filling it up with treats, but the younger dog plays with it even when it's empty.
My only frustration is that the dogs don't want to share it! If you have multiple dogs, make sure you supervise them during playtime, and keep an eye out for resource guarding behavior! One of our dogs is very submissive, and this is the ONLY toy she's ever refused to give up to her big brother. I'm going to need to get another Scratch Square to make sure his nails stay short, too!