Sidecar is working beautifully now with Catalina Public Beta 3, along with my iPadOS Public Beta 3 iPad Pro 10.5".
Is nice to have dual screen support for my work (eg. PowerPoint), with just 3 lbs of devices.
Well, it works perfectly via Bluetooth or a wired connection. With a WiFi connection I lose WiFi internet access, and sometimes it lags hard. It's weird. With WiFi, it may work perfectly one minute and then the next minute it feels like a laggy Remote Desktop Connection session over the internet, really bad. Both devices are connected to the same Apple AirPort Extreme 802.11ac access point sitting just 2 feet away on the same desk. (I say access point, because the actual router is another AirPort Extreme in another room.) But I'm fine to use wired or Bluetooth, so I'm happy, esp. since the image quality is excellent.
This is on my 2017 MacBook, but it should work as well on the 2016. For those with the 2015 MacBook, yes it can be enabled, but reports continue to say that image quality on such unsupported machines is terrible. Furthermore, it's unstable on unsupported devices, so IMO it's pointless to try to use Sidecar on the unsupported 2015.