The Good: ~Spools-up extremely fast
~Sub 210g weight is consistent
~Incredible wear, from machined, inner 8 cogs
~Smooth, instant telepathic shifts, rivals Shimano XTR
~Materials science at its finest
~High resale value
The Bad: ~Pricey
~SRAM lied about replaceable 36t cogs, in their ad campaigns
Upgrading from my hefty, 355g SRAM PG-1070 cassette - the 207g XG-1099 spins up so fast, it's almost like losing four additional teeth on your granny chainring. The 148g difference CAN BE FELT...the moment you spin the cranks. Climbs that normally petered me out can finally be cleared, due to the reduction of rotating axial weight.
If you are strong enough to stay away from using the alloy 36t cog - you can also expect 3-4 seasons of hard trail riding, on this cassette. Just be sure to religiously monitor your chain wear and this cassette will easily outlast many lower-end cogs by 3:1...making this component a decent value(somewhat).
Currently, the only aftermarket maker of replacement 36t cassette cogs is Experimental Prototype, in Sweden. SRAM decided it unprofitable to offer replacement cogs, after all the hype about making them available. They simply lied...