Thought I would leave a few comments on my experience with IINA as a VLC replacement for me.
First off, I've used VLC for quite a few years, however it's always felt a bit quirky and a bit unstable. Second: I do realize the VLC does other functions besides a player, however with this said, I've never personally used the app for other things then a media player, so my comparisons won't include those features.
I started using IINA around the time VLC 3.0 was released due to playback issues I was having with VLC, such as the A-B loop not always working correctly in VLC, features like variable speed control in playback also doesn't work reliably in VLC 3x.
Other things I've compared, are Videos with strange resolutions, now act jerky in VLC 3x.
With the above listed, I have found IINA is quick to load video files, plays what I throw at it very smoothly, and without graphical glitches, the A-B loop is much more reliable. Videos with unusual resolutions don't jump around, or flicker. I also feel comparing the two, that IINA, has a better macOS native interface vs VLC, and a cleaner, more optimized and up-to-date UI.
I have a few media players installed on my Macs, as none are perfect, and it helps to have more then one installed in case one might not work as expected, or another one has a feature, one might now have.
My other Media players I have installed are:
El Media Player (pro version)
Blu-ray Player (Pro Version) from MacGo.
As far as the Blu-ray player, it's a good solid player that gives commercial grade support for playing back commercial Blu-ray discs as you would in a hardware stand alone player.
As far as the features people have commented on here regarding VLC being more then a media player when comparing IINA to a replacement. That i'm not going to disagree with as I know it's true. What I will say though, is for my own use, I have not used VLC for those functions, and probably never will. I have always used dedicated apps for Video conversion, and recording. ScreenFlow is my main recording app, and FF Works, or permute are my main conversion apps, I do own the Apple pro apps as well.
With all the things I've listed above, here is what I feel a good verdict is:
If you simply use VLC as a player, and nothing else. IINA is a great replacement.
If you use the other features it offers, I can't really make a fair comparison here. I would recommend comparing VLC to a dedicated app that handles the functions desired for use.
In the end, I think IINA is a very nice solid player all around. I've had no issues with it, and it has some nice bonus features like a command-line tool, that can be configured, and a browser plugin for both Firefox, and Chrome. Safari support was removed when Apple's plugin requirements changed.