From what I can see, Mirage is a fairly decent remould to make it more "Earth mode" than the Cybertronian mode Siege toy... with several new parts, and the back end of the car mode is transformed differently, so that the spoiler/arms are further back and pointing backwards in car mode.

It's a bit like Netflix Bumblebee... it's a new-mould/significant-remould of a major character that I think should be in the mainline.
Meanwhile, the more obscure character of Beast Wars Grimlock (and this toy doesn't homage that original toy very well with it lacking the right paint details), deserves to be in a small-run exclusive release like this... it is just a shame that the people wanting Earth mode Mirage, have to buy a Voyager Beast Wars toy to get it. (there are more Gen1 fans than BW fans, so Mirage would be the more sought after figure of this pair)