I had a 4506 (I know this about the 645). It never felt right to me. Tall and thin, felt like the only thing my grip was in contact with was the front and rear straps. Sights on mine were off quite a bit, high and to the right.
Solid, robust, and yes it would feed an empty case, but so will my 1911's (never shot an empty case anyway).
I wish I could have warmed up to it. Sold it.