The bottom is actually crenelated and with the internal ring can actually serve as a bottle opener. Hard to explain but if you handle one you will get the idea. It is made from one solid chunk of aluminum, not cheap. Also the process to get the end result from that solid chunk involves a bunch of material removal and machine time.
The fact that it is a large hunk of aluminum means it actually keeps the liquid in it pretty cold for a fairly long time. When I was trying one out we poured in an ice cold corona (only think available at the time) and it stayed ice cold through some pretty long conversations at the shop after a product testing day on the range.
Are they neat? You bet. Are they exceptionally well made? Certainly are. Do they function as designed? Very much so. Would I spend my hard earned money on one? Not a chance, but then again I am more slow speed, high drag.
