[...] but none of them are as simple as they should be and most don't seem to work as expected if at all. [...]
Unfortunately, "simple" is a matter of perspective.
That being said, I know of two programs that do what you want.
The first, FileMeta
a helluva lot more overwhelming than it actually is.a program to allow use of the optional tags displayed by windows explorer
To create an example, I chose ".ahk" files and added "system.keywords" (tags) to what is displayed and what I can edit in Windows Explorer's "details pane".
Here, you can see that's I've set the focus to the "Tags" field.
I didn't add a tag because I forgot to and I would go back and re-do it, except I'm sitting outside getting eaten up by mosquitos and if I get up and go inside, I'll never finish this reply. So I'm suffering the loss of blood to small flying creatures, as I hurry to finish this reply.a program to allow use of the optional tags displayed by windows explorer
The second one is Windows Property System View by Nirsoft
I haven't tried it, but it looks simple.