Hi 
The short answer is yes. You can trust the OU in this! 
Alex Thergood is more expert with Macs than most of us here. He is one of
many people on this mailing list whose advice i trust and take a lot of
notice of.
You do need a separate emailer. Many people seem to use Thunderbird but i
am not sure what people tend to prefer on Macs.
In more and more detail ...
LibreOffice has all the functionality you or anyone else are ever likely to
need.
Almost invariably when people or magazine articles attempts to claim
otherwise it's because they haven't tried, haven't even googled "how to",
nor read any documentation (available free), nor asked any of our or other
user support systems.
https://wiki.documentfoundation.org/Documentation/Publications
LibreOffice is free and easy to install on all the various systems
currently in common usage for such work. It is also highly compatible with
a wide range of other programs - to an extent that even different versions
of MS Office are not quite compatible with each other! So if there is
anyone who still can't use 'our' format it's quite easy for them to use
Google-docs or even download and install OpenOffice/LibreOffice for free
and with little effort. It's a bit like if a system can't read a Pdf! 
LibreOffice does have features that MS Office lacks - and along with
OpenOffice (and many others) has, by it's very nature, many capabilities
that MS Office either lacks completely or that would cost a lot to add to a
standard MS Office bundle. There are many add-ons/plugins, we still call
them "Extensions" rather than use those new-fangled terms! 
One feature is that you can use an iPhone or Android phone as the remote
control device for presentations. Also it is easy to change all the menus,
dialogues and pop-ups to one or more of over a hundred human languages.
The OpenSource ethos is quite different so occasionally things are called
by a different name and/or appear in a different place in the menus. We
share that ethos with many other programs and it's similar to the ethos of
OpenOffice. The ethos is a bit different from Google-docs but not hugely
so. So, once you get used to such a non-MS program then you'll find you
are much more able to change to others or swap around using different ones
to suit different circumstances.
Macros can sometimes be a problem but since the OU has said that
LibreOffice is suitable they will have taken that into account. Many
places manage to totally avoid using macros anyway. MS macros have so
often been used to infect machines with malware that many places block all
macros. Again MS macros often seem a bit incompatible between different
versions of MS Office. I've worked in offices for over 30 years and never
used or needed macros.
Compatibility issues are often talked about in the Microsoft world because
MS seems to constantly create problems around this issue. Each version of
MS Office uses a different "transitional" version of their OOXML format and
this forces people to keep buying different versions of MS Office in order
to remain compatible with each other. It could even be seen as a marketing
ploy. This seems to be true of macros too, as well as formats.
You wont have to worry about this though because the OU has stated that
it's Ok to use LibreOffice and our format stays the same throughout all the
various versions. So you should be able to easily share documents with
other people, and if anyone struggles then they can download and install it
for free anyway.
It is not really accurate to call it "our" format because it is an ISO
format that is developed by a world-wide organisation that is comprised of
a vast number of different companies (and individuals). So unlike
Microsoft's ever-changing formats it doesn't keep changing at the drop of a
hat. So the "LibreOffice" format is also the "OpenOffice" format, is also
the "Calligra" format, is also the "KOffice" format, is also the "Abiword
and Gnumeric" format, is also the IBM Lotus Symphony format, and on and
on. The documentation describing the format is freely available to anyone
= so even far off into the future almost "any Tom, Dick or Harry" could
throw together something to read and use the format. The MS formats
(including their old Rtf format) is not future-proof in this way because
even their own implementations of their own formats is a bit different from
the way they defined it - and inconsistent between any 2 versions of their
programs.
While almost everyone else has been happily using 'our' OpenDocument Format
1.2 for many years Microsoft decided to try implementing the older ODF 1.1
instead in their 2007 and 2010 versions. Although everyone else seemed to
find it very easy to write code to use that format for some reason MS
couldn't quite manage it and botched their reading of ODF spreadsheets
really horribly. They have promised to have ODF 1.2 in their 2013 and
their "365". However MS have made similar promises about
"interoperability" for decades and they somehow don't even seem to manage
compatibility between their own programs very well. Almost everyone else
manages a much greater level of compatibility without making such a big
fuss about it. Apple apparently removed ability to use ODF in Pages in
January of this year, just as people seem to be freely using the format
much more widely when sharing documents. If they reinstate it then Pages
might become much more popular but being unable to handle both the main
formats seems a bit arrogant/dumb, especially since Pages is such an
extremely low priority for Apple.
Everyone (even Apple) can use the old MS formats originally used natively
in MS Office 2003 and earlier;
.doc rather than .docX - for Word processors
.xls rather than .xlsX - for Spreadsheets
.ppt rather than .pptX - for Presentations (at least for ones done using
an office suite rather than some dedicated program)
These currently seem to be the best formats to use when sharing between
almost anyone, even between people using different recent versions of MS
Office.
For most programs, certainly for LibreOffice, just go to the "File" menu
and down to "Save As ..." and then choose the "Microsoft Word (or whatever)
2003/Xp/2000". Those numbers at the end occasionally change but as long as
it's 2003. This is all far tooo difficult for most MS Office users to
understand and that is why people keep going on about "compatibility
issues".
I have had a lot of success sharing documents in ODF as the format is
becoming MUCH more popular quite rapidly nowadays but if i know someone is
limited to only some old version of MS Office (or Pages or some-such) then
i use the old MS formats and sometimes i use it just to be certain.
Blimey!! MUCH more than you needed to know!
Regards from
Tom 