Welcome aboard
In regards to your predaking question, the hasbro platinum editon predaking appears to be a straight repackaging of the predaking boxset which was reissued as part of takaratomy's transformers 2010 range.
As for cosmetic differences, from the few images ive seen, the platinum edition appears identical to the 2010 reissue which included changes like gold plastic and paint replacing the yellow, metallic fleck in the red, orange, black, gray and a new sticker sheet including ones for the eyes.
The main difference the platinum edition has over the 2010 reissue is the sword supplied for predaking. It's much more in scale than razorclaw's sword which was used with the original, 2004 & 2010 reissues