I have a stainless one and an aluminum one. The stainless one is from Ebay, and there are plenty listed at any given time. The aluminum one is from Virgin Valley Custom Guns. It was bought (and the other one has never been used) because I read on this forum that a hammer extension can sometimes weaken the hammer spring and cause it to break, causing misfires. I was assured that this would not happen with the lighter weight one, which is why I bought it.
I feel as though my extension is necessary. There is not enough room between my pistol scope and the hammer to get a firm hold with my thumb for a let down with out a possible slip and accidental discharge.
Regards,
Smoky