So, I'm looking into getting a 50mm prime lens. I was going to go with the cheapest $100 1.8 model instead of the $300 1.4 model. Then I saw a lens that had a really nice looking build quality similar to the 1.4, but was only a 1.8 http://www.ebay.com/itm/Canon-EF-50mm-f-1-8-Mark-Mk-I-Metal-Mount-Camera-Lens-EOS-DSLR-/111280614494 Are there any drawbacks to this instead of the normal 1.8 canon lens besides the price increase? Pros? Cons?