The advantage is that they are faster and easier to apply than chains. They say that you can install a pair of Spikes Spiders in less than one minute. Also you do not have to lay down on the ground to access the back of the tire like chains. And they don't get tangled up.

The disadvantage is price. Les Schwab wanted $300 a pair for my 255/55 R18 tires. At the time I didn't know they made more than one model so I didn't ask which model they where quoting me a price for.

Below is a link to the installation videos. It looks really easy to use.
http://www.spikes-spiders.com/videos/