Yeah foobrew, I had seen those types of contraptions too. Works great for hops, but seemed over-engineered and would be awkward when it's time to drop the immersion chiller in.
I liked the perceived durability of the tea-balls being stainless and - and yes, concerns about enough 'flow' through the ball for good alpha acid extraction we in the back of my mind, thus wondering about what size\how many to get.
However, the inconvenience of having to pull it from the wort, open it (coated in very hot wort), drop in more hops, close and re-immerse have prevented me from getting one (or two) *just* yet. I may visit the local Asian market and see if they've got some I can look at in-person. The security and ease of operating the clasp could make or break it for me.