I have not used Tag (or Max for that sake) very much but I'd thought I'd share some opinions on the UI. And I think I'd better do it before my initial impressions become corrupted.
1) Main wIndow has no red "shut window"-button. Annoying. To shut it you have to quit app.
2) Too many actions in both Tag (and Max) are performed only from top-menus. You should have for ex Save and Open file buttons in the main app-window. It's for ex NOT intuitive to execute a change in tags only via pressing the Return-key (and BTW what is the difference between return key and Save?). It's good the opportunity exists for key-board enthusiasts but not for newbees. Altho I have used computers since 17 yrs (I started with the mac and been faithful to the platform during all this time) it took me some while to figure out how to make tag changes stick. This sort of behavior is not what you'd expect in a mac-app!
(Album art in Tag is long missing...)
Altho the above I am of course very thankful us mac-users have these 2 apps.
UI quirks
Re: UI quirks
In sbooth.org applications there are indeed a few GUI quirks. The most notable I find the need to hit TAB or RETURN to make a value entered in a dialog box stick. This is unusual in Mac applications, in fact I only encountered this behavior in sbooth.org applications. And, yes, the missing close button in the Tag window is annoying
Re: UI quirks
Having to "tab out" of a field may not be exclusive to Stephen's apps.
I first encountered it in Osiris and the developer said it was an Applescript thing.

I first encountered it in Osiris and the developer said it was an Applescript thing.