The Parker 100 is much more than a Parker 51 on steroids! Clearly Parker intended to hark back a few decades to the 51 by using the same overall shape and hooded nib but the similarity more or less ends there. With it's all metal construction, deep lacquered finish and larger size the 100 is a much heavier and more substantial pen than the 51. Whether or not this is a good thing is a personal choice but few can doubt that the addition of an 18Ct. gold nib and more opulent use of materials adds something to to the original.
I am a huge fan of the 51, it is a great pen in every sense, and I think the 100 was a brave attempt by Parker to modernise, and cash in, on the success of the 51. What they produced was a remarkable pen in it's own right that should be treated as such. I think it is a far better pen than the Parker 51 'Special Edition' and leaves the 'New', 2021 Parker 51 dead in it's tracks.