I would say the
El Bolso bag is worth it based on individual factors coming into play. The purchase of this bag seems to depend on you, your enviroment you ride in, and if you need something to roll up into a compact pouch that a speciality bag for folding bikes was specifically designed and intended for. Actually I own and use several bags for all my folders. I have purchased huge duffle bags which I store the bikes in when not in use at home. I have bought Dahon's own
Double Play bag (no longer available) when I bought my first folder. I like this bag far better than the El Bolso one. And I have and still make my own bags myself whenever the need/mood strikes. For the bag and it's pattern see:
http://www.flickr.com/photos/world-of-folding-bicycles/988690181/in/set-72157601331380862/