The 99 Classic is a FUN headphone to listen to (here used with a Mojo 2, Roon and Quobuz/Tidal HD services).
I really wanted a 109 Pro, budgeted for them and expected great things but after hearing them at the Bristol show with up to £2.5k of HP amplifiers left disappointed. I then listened twice more at dealers (with my Chord) thinking all those reviews can't be wrong but ... .
To me (!) the 99 Classics clearly have the upper hand. There is a solidity, rhythm and fun to these the 109 just can not match, not even close. The 109 Pro do sound a little more spacious, unsurprisingly, they are open, but they also sound flat and uninspiring in direct comparison. No drive, not much fun and PRAT (pace, rhythm and timing for Naim afficionadas).
I have a pair of Sundaras, they do open and detailed whilst still sounding more animated than the 109 Pro.
Shame. I really (!) dig the looks and build quality.
I would have bought the Lyrics which sounded superb and (to me) are the real upgrade to the 99 but they were a little bit too expensive at the time due to other expenses.
As is, the 99 Classic (and I guess the Neo though I never heard them) are good headphones in the 250$ range. They have unusual looks and different sound to other good alternatives. Not necessarily better but different enough to make them viable alternatives. The build alone makes them worth the money. Lovely wood and metal, silver in my case.
I am no HP 'expert' though. These are merely my own impressions.
My other f/s HP's are the afromentioned Sundara, Beyerdynamic 700 Pro X, Grado SR80X and Beyerdynamic HD58X Jubilee. I use these with a Mojo 2 or Hegel and Audiolab amplification.
I also use some Samsung Galaxy Buds Live (the 'beans') for out and about/holidays. I got a pair of the successors, the Pro's but sold them on immediately. Not on the same level. After nearly 4 years of use the 'beans' still keep charge and work like new! So good I think they are I bought another pair some time ago for when the originals finally give the ghost up. Superb and I never ever feel I give much up vs. the others.