Hi guys. I just wanted to report back on my Ubuntu/Mint confusion. After a 9 hour drive home yesterday, I've spent nearly that long today installing Mint and Ubuntu numerous times side-by-side on two different UEFI laptops, one with HDD and the other with SSD. As @wizardfromoz noted, these distros can coexist just fine, as my own experience proved to me today, both with Secure Boot disabled and also with it enabled. It also worked fine choosing both "install alongside" or "something else" in the Ubiquity installer. I also installed Mint first, and Ubuntu first, to see if that was the issue. I was basically trying to make it fail, but it didn't (except for a few wonky cases with the HP laptop, because it is a stubborn beast anyway).Safe travels and I look forward to it (your Ubuntu experiences), I AM intrigued.
But to make sure you know I was not hallucinating about this issue, I'll also let you know that this fear of installing Mint and Ubuntu together came from a very reputable source: J.A. Watson, a tech writer who contributes articles frequently to ZDNet and others. He has actually harped on this issue for several years at least, so it must have settled into my brain as fact as I read his reports. Some examples:
From June 2014: "Oh, one last comment about UEFI boot to close this post. As was the case with the previous Mint 16 release, the UEFI boot directory will be named 'ubuntu', so if you want to install Mint 17 and Ubuntu both on the same UEFI boot system, you will have to be careful about that. The most obvious solution, renaming the boot directory after the first of them is installed, doesn't work (it won't boot that one any more). The solution I have found which does work is to create a second EFI Boot partition, but neither Ubuntu nor Mint will let you specify the UEFI boot partition to use on installation, so you have to copy the boot directory to the second EFI partition after installing. This is not a big deal, if you are "advanced" enough to be installing both distributions on one system, then you should also be able to handle this."
From January 2017: "As I have mentioned many times before, one of the unfortunate side effects of this is that Linux Mint uses the same EFI boot directory name as Ubuntu, so if you plan to have both of them installed on the same system, you have to make some special allowance for that. As this Mint installation is the first of the two I will ignore that for now, and deal with it later when I install Ubuntu." (Except that he did not return to this problem in this article.)
He has referred to this problem in the intervening years, and was apparently experiencing problems even before 2014. So I was convinced he was right, and his argument made perfect sense that using the same bootloader location could be a problem (/boot/efi/EFI/ubuntu). I don't read his articles regularly, but I have run into them often and I enjoy his friendly writing style. And he certainly seems to know what he's doing... so I'm confused as to how he has not realized before that these distros can work together.
Oh well, enough of that. My apologies for the diversion.