Something I was not expecting but greatly appreciate is how well "matched" the Worker flywheels are (basically how physically similar they are). They are significantly better matched than most Nerf flywheels I've come across (presumably through more precise manufacturing), and so produce a noticeably quieter and more harmonious noise. A well matched set of flywheels also provides a minor performance benefit compared to a poorly matched set of flywheels, in both muzzle velocity and accuracy.
One of the big benefits of Worker flywheels is an increased muzzle velocity, provided you have proper motors with a proper power source. A comprehensive post on Britnerf has a good amount of data and observations, and their data agrees with what data and experience I have. Said post recorded a muzzle velocity increase of ~15fps on average, and while I don't have proper data of my own to refer to, I can say that darts do fly out noticeably faster with Worker flywheels installed.
Another big benefit I saw was accuracy improvement. Previously, my Bullpup RS could achieve a spread of over a metre at just ~8m range with Kooshes, which is horrendously large and made it a nightmare for mid range combat. Switching to Worker flywheels saw the spread reduce to a little more than half a metre from the same range and darts. In the first event with the Worker wheels installed with FVJs, I saw a massive improvement in effective range, and was able to effectively engage at significantly longer distances. This accuracy improvement combined with the increased muzzle velocity make a Worker flywheeled blaster substantially more effective in combat.
The main disadvantage to the Worker wheels is that by virtue of the toothing, they tug on darts more aggressively than stock flywheels, and in particular love beheading weakly glued Kooshes - before I found a good Koosh glue, I was constantly beheading probably a third of the Kooshes that I fired (I now use Selley's Shoe Glue, and it works incredibly well). I also noticed greater wear on FVJs, just behind the tip. It's something to watch out for, especially if you use darts with poor foam or weak tip glue.
An additional interesting data point is the performance of Worker flywheels at excessively high speeds. One of the players in the Melbourne groups has XP180s on his Rapidstrike for flywheels, and runs them on 3S with Worker flys. This is excessively fast considering XP180s already get glass ceiling velocities on 2S, however the player has reported getting 10-20fps muzzle velocity gains running on 3S vs 2S, and only with Worker wheels, as stock flywheels on 3S just burn darts.
It is worth noting at this point as well that while stock Nerf flywheels build up a foam residue over time through use (which improves performance and reduces dart wear), Worker flywheels do not build up any residue whatsoever.
Worker flywheels are available on Taobao (basically Chinese eBay) for 40CNY, however unless you live in China, you'll have to organise additional handling and postage to get it to you. It cost me 30AUD for two sets including all extra fees using Buychina, one of many Taobao "agents". Overall I'd highly recommend Worker flywheels on any top notch flywheel blaster build (assuming they're compatible of course), the performance improvements and out-of-box matched flywheels make for quite significant improvements over a stock flywheel build. Worker wheels should only be added after motor replacement however, new motors with a proper power source give a far bigger performance improvement, and given how much more friction they appear to add to the system, Worker wheels may actually be detrimental to a weaker flywheel build.
I will certainly be putting Worker flywheels in any of my future flywheel builds that I intend to use a lot, unless a superior flywheel or blaster system presents itself.
Something I would like to see is a smooth concave aftermarket flywheel, as I'm not sure if the toothing is actually necessary. I would be interested to see if a smooth concave flywheel could achieve similar performance without the extra dart wear.