I bought the 10-pack, not because I need 10 of them, but because they make great gifts.  There's not much to say about these.  They're plastic, seem durable, and do the job of keeping your tie from shifting side to side, accidentally turning around, or hanging down when you bend over.

Tie Chains and Pins do the same thing, but if you want a cleaner, no-bling look, these are perfect.

Update - April 2015:
They aren't as durable as I had expected.  They start to crack in the corners of the rectangle button hole, which will eventually break open.  I use these approximately twice a week, and have worn out several of them. The price has gone up considerably since I purchased them.  I've switched to a cheaper alternative - making my own from large paperclips.

Design change recommendation - instead of having four 90 angles to make the rectangle shaped button holes, make the ends rounded (long oval).  This will prevent the cracks from forming at the corners, and will make the device more durable.  Do that, and drop the price to less than a buck a piece, and I'll definitely buy more, and recommend them to others.