I mostly use the Mac version and the main features for local playback of audio files work flawlessly like on Windows.
Since your friend is on a Mac and may see there is an option to sync old iPods, which does work on Windows, you may want to let him know this does not work on a Mac. If he is expecting he can sync any handheld Apple devices (iPhones, old iPods, etc) it would be useful for him to know that's not possible.
If he sends audio to more than one Airplay device at a time, something Mac users may take for granted via iTunes for past few versions, there may be a way to do this in JRiver via dlna but I've never done so. However, it is easily achieved with third party software which I use to stream my JRiver playback to an old Airplay device while simultaneously playing through physically connected speakers.
I've been using JRiver on Mac for a while now and pretty much stopped using iTunes at same time. I tried another program that was more Mac-like in appearance / interface, but soon settled on JRiver because it has more features and is much more customizable, and because it is cross-platform which is beneficial to me.
There is also the ability to import an existing iTunes library, I believe, which I think will bring over play counts and playlists so if he has been a longtime iTunes user that could be great. I don't know if it works on the Mac version.