Disclaimer: I'm the developer for the app mentioned below. I apologise if this post is against forum rules.
So… is desktop tethering an important thing for EOS M users?
I make
this tethering app for iOS. It supports all Wifi-enabled EOS cameras, including the M3. While the UI of the app is iOS-only, the underlying connection stuff already works with Mac OS, and I have a very terrible-looking app for Mac I use for testing. While it looks terrible, but I can use it to shoot tethered to the EOS M3 right now.
I've been toying with spending a couple of months to polish up and release a Mac version of the app, but I figured with the number of tethering solutions available on the platform and that mine only works with network-enabled cameras, there wasn't much point.
As for speed, the WiFi on the M3 is reasonably quick for in-camera WiFi. A 31Mb RAW file transfers in ~13 seconds.