@CGB If you wish to single boot Ubuntu MATE without using rEFInd, which probably gives you a substantial delay during boot 
, you can have a look at a Q&A style tutorial that I had written on Ask Ubuntu - EFI boot Ubuntu 14.04 on a Mac without rEFInd . Since the method uses EFI boot and has faster boot times, it should work better 
. It works for Ubuntu, so it should work for Ubuntu MATE too…
Regarding the Wireless issue, it is a problem on all Ubuntu releases and flavours since the Broadcom wireless chip does not play well with the open source drivers and needs the bcmwl-kernel-source package to be installed from the repositories.
@Wimpy We can probably have an official tutorial for this topic. Many people who prefer Ubuntu MATE over OS X can replace their operating system without having any issues…