Here's the Dobro Hound Dog. It's a fun little guitar. The stock pick-up leaves something to be desired, in the volume department. That said, this guitar does have it's uses, the main one being- it's fun to play.
The resonator guitar was originally designed to help guitarist's be heard in band ensemble situations, prior to the widesoread usage of electric guitars and amplification. The main design feature is an aluminum cone underneath the bridge, inside the body of the guitar. The idea was the cone would act as a 'speaker'. Not being around in the 1920's and 30's myself, I'm not sure that the design ever really succeeded in it's intended roll.
The enduring aspect of these guitars is the tone. They seem to have found a permenent home in bluegrass and the blues, and slide players love 'em!