I like the isco, but it is a beast. Most of it is metal (brass I'm assuming), but it does give a tack sharp image. However, it is a newer lens and doesn't flare easily because of the lens coatings. If you're after a lens flare, I'd avoid it. Also, it's color and hugeness really makes it conspicuous if you're stealing shots or doing any guerilla filmmaking.
Kowas are a good alternative, despite the price. Much smaller and easier to run and gun with (as much as you can call double focusing anamorphic run and gun...:)