I have the Snap on 3/8 drive wobble plus set and most of their 1/4 drive wobble plus set. They're very handy and take up less space than having a regular extension set and some wobble extensions on your cart. As for reducing the overall length of a socket/extension setup, the difference is minimal. To go from wobble to straight, the socket is pushed further on to the extension so that the square area above the wobble cutout contacts the female drive part of the socket. They are handy. Are they worth the money? Without starting the usually brand war, they can be to the right person. It is nice to able to switch from straight to wobble by moving the socket slightly without having to switch extensions.
However, Sears sells similiar extension sets under their Companion line. They are similiar in the fact that they are extensions, they have knurling on the shaft, and feature the wobble plus design. They can be had for less than $10 for a 3 piece set. I am not saying that they are equal to or better than the Snap on versions. However, if you wanted to try the wobble plus type extension out, you could do so with a minimum investment at Sears.