The Index Percussion Accessory (IPA) is the original steel can shaker made from vintage Beer and Soda cans from a bygone era. The 12oz is the standard size, and is perfect to throw in a stick bag. They are much more durable than modern cans, with thicker walls and a stronger shape.
The "hoppy" flavor is a more traditional shaker tone, with nice attack and volume, with a rich metallic sound and lots of depth.
The "smooth" flavor is much quieter, and more suited for small venues. If the "smooth" is a 3 and the "hoppy" is a 7, the "Bonzo" is an 11.