I'm surprised nobody has mentioned MyWhoosh. Apart from the naff name, it looks like the rising star to me. Anyone tried it?
Yes, 700km+ so far. Less users, so find the (race) series that runs regularly each week. But don't expect more than 20-50 riders in each race (might change now!). Check
https://results.mywhoosh.com and find the series with many participants.
No categorization check in normal (race) events, so you will be racing a mix of "Zwift" A-D riders. Some races have at set limit (in their title), but AFAIK there is nothing stopping you from joining a lower cat.
If you want proper racing with little chance of cheaters, do the
Sunday Race Club races with real prize money to be won... Just be aware that you have to supply weigh-in videos and dual recording for each event!
Up until recently the main barrier for MyWhoosh was the somewhat steep PC requirements. But with the release of the "MyWhoosh Go" version recently, even those who uses old PCs (or office laptops) will get an OK experience.
Apple TV version is also released (or close to final release?). The whining has stopped on the MyWhoosh pages, so I guess the ATV-people is happy now? Amazing how loud/annoying they can be about when a
free platform will support THEIR low-end device, instead of themselves buying a device that can handle that platform (and all others too)...
The draft on MyWhoosh is different (less), so the exagerated speed of Zwift is not there, meaning doing something like the Rapha 500 will take longer.
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