LoopTools is part of my blender bread and butter, the moment i learned about this tool my whole pipeline changed, i just can't install a new blender profile without this!
Hits the mark every time I need to work on MMD models, can't have blender without it
If your working with VRM models you really can't go wrong, it helps with all the nitty gritty things that you just don't need to think about anymore, it's become a staple of my workflow