Mesh Check GPU Edition,  right in the viewport, everything that gets in the way of a clean mesh.

• Ngons
• Triangles
• N-poles
• E-poles
• Poles with more than 5 edges
• Isolated verts
• Non-manifold edges

Built for large meshes. Version 1.0 is a complete rewrite on numpy: nothing is recomputed while you orbit, only when the mesh actually changes.
A vertex move on an 80,000-face mesh with every check on costs 10 ms, where the previous version needed 400 ms per redraw for the triangles alone.
A draw limit keeps the counts but skips drawing when a check flags too many elements (a print-ready mesh is all triangles).

See through the mesh. Show Hidden draws the highlights hidden behind the surface, fainter, so you can tell what is in front from what is behind. X-ray works too.

Works on one or several selected objects, in Object and Edit mode, on the object's own topology (modifiers are not taken into account until applied).
Per-object statistics, custom colours, everything in the viewport's Overlays popover.

The display color is customizable from the addon preferences.

The mesh_check_gpu_edition_V1-0-0 version requires Blender 5.2 or later.

Older versions, compatible with Blender 2.8 to 4.x, are still available in the files.