Anyone try a Vivitar 2x extender

[K-amps]

I know... you get what you pay for... but at $109, this is worth looking into: I was wondering if anyone has any experiences with these: http://www.ebay.com/itm/2X-Extender-Canon-EOS-EF-II-Lenses-/130621881929?pt=Camera_Lenses&hash=item1e69abbe49