most are 2-4". some smaller, some up to a foot+. i would like to see a video of that also. seen em on tv smacking lab tanks. very loud. if i had a SW sump/fuge, i would definitely have one of those in there.
i've seen some nice 2g-5g nanos with a little reef and a mantis online. pretty cool substitute for a betta if looking for a "fish" to keep at the office.
If I remember correctly, there is a guy who makes vids about his shrimp. I believe he calls it "Lord Damage." I dont think he has vids of it breaking a tank, but he does have some hunting vids.