Mesh Check GPU Edition is an addon that helps clean up geometry in Blender by flushing out problem elements. It detects ngons, triangles, N-poles, E-poles, poles with more than five edges, isolated verts, and non-manifold edges. The addon works on a single object or a selection, in both object mode and edit mode.
The display color is customizable from the addon preferences, and an X-Ray option lets you see the flagged elements through the mesh. Mesh Check is also handy before exporting an asset for 3D printing, where it can check whether a model is closed. You'll find it in the Overlay menu of the 3D view.
Published by Pistiwique, the addon is compatible with a wide range of Blender releases, from 2.8 through 3.6, and is distributed under the GPL license. It carries a 5-star rating from 6 reviews on Superhive.