A bit of my on wheel history for perspective: I've ridden both clinchers and tubulars, various tires and both butyl and latex tubes. Road wheels: Ksyrium Elites --> DT Swiss Mon Chasserals 1450 (still have them) --> Zipp 303 tubulars --> Zipp 404 tubulars --> Zipp 404 alu clinchers (still have them; they're for sale on the classifieds) --> Neuvation R28sls (still have them). Have also ridden clincher and tubular HED3s on TT bikes, but I'm purely a road rider nowadays (sprinter type).
Picture of the bike with wheels below. I've got Panaracer R'air tubes under Continental GP4000s tires. Wheels have been de-stickered to match my bike (an MC053 built up mostly with SRAM Force).
Firstly: these wheels are fast. Not the lightest wheels; my DT swiss wheels and Neuvation wheels (as well as Zipp tubulars) feel lighter in terms of acceleration, but not by much. Accelerating on these wheels do feel faster than my Zipp 404 alu clinchers though. In terms of holding speed, they do better: rolling at 22-23mph is rather effortless on the flats. Feel slightly slower than Zipp 404 alu clinchers, but again, not by much.
These wheels are certainly stiff though, stiffer than the DT swiss and Neuvation wheels. Because of the wide rims and the older-generation SRAM Force brakes, I've had to set up my brake very close to the rims - they touch the rims with the slightest pull, rather than 1/3 of the way like I usually prefer. Despite how close they are, the brakes don't rub at all in a sprint. Acceleration on these wheels feels solid - not snappy, but solid. To be any snappier, I think you'd need light tubular rims.
Most importantly, these wheels are *comfortable*. These wheels feel a lot more like my commuting wheels (with 700x28c Panaracer Pasalas on 29er rims) on my commuter than my other aluminum road wheels (which both have GP4000s tires and latex tubes) - bumps on the roads are just muted. I was actually actively looking for bad patches of road to go over just to see how they felt like (not much at all), while on my other wheels, I'd normally actively avoid them, and brace myself for how much they'd jar me, especially on my boneshaker of a road bike. These wheels actually made a stiff overbuilt carbon bike feel comfortable.
Bottom line: These are the ultimate do-it-all wheels for the amateur road racer on a budget. At $500, it'll be a wheelset that you would dare to race in crits (and yes, the grip feels pretty good on these wheels, although given that i was riding on new tires, I didn't push it) without slowing you down too much when the road turns upwards. It'll be comfortable for training, and will leave you fresher for the end of long hard races. For almost a third of Zipp 101s (which would be the most comparable wheelset out there right now).
For the majority of my ride, I was thinking to myself: SRAM should just acquire Flo wheels, Quarq style. Would be the perfect platform to test out direct-to-consumer internet marketing, Flo Cycling would get the supply chain management that it so sorely needs to grow its business, and we all get a chance to get and ride Flo wheels. Everybody wins. With SRAM on board, imagine selling complete ride-ready wheels to directly to customers over the internet, already shod with tires and cassettes installed. I suspect this will be appealing to many potential consumers, and would broaden the customer base to one that includes the less mechanically competent.
Slowtwitch Aeroweenie since '06