I see that, in addition to a Mac version and a Windows version, there is a “combo” version of Scrivener. What’s the purpose of this? I see it costs more than either of the others.
I ask because I am an editor with Windows working on documents created with Scrivener on clients’ Macs. Some of the functions the Mac version offers (e.g., Revision Mode) do not appear on the Windows version. Would it appear if I got the combo version?
This isn’t a separate version, but rather simply a regular copy of the Windows licence and a Mac licence. It wouldn’t be useful in your scenario, but if say you had a Mac laptop to go with your PC, you would probably want the combo bundle so you could install it on both machines.
Here is a list of the major differences between platforms: Differences Between the Mac and Windows Versions. The disparity is down to the Mac version being an older program, Windows was introduced years later and is still catching up.
Specific advice for revisions: use the “Snapshot” feature if you aren’t already doing so, prior to editing a section (Ctrl-5 or Documents/Snapshots/Take Snapshot). Not only will this retain their original text as a reference against your edited version, on the Mac there is a feature that will visually compare a snapshot with the current text using proofing markings (and yes, that will be coming to Windows as well 
). Although it lacks the whole review procedure in Word, this gives the Scrivener user an effective way to “track changes” between drafts.