I mainly use Openscad, which works like my brain, but is really poor in terms of measuring or confirming sizes in STL files. Especially when all you have is the STL file.
Today I discovered Meshy (Meshy). What a life saver! Web based, no install. Just a shortcut in my 3D folder.
Simple import the STL, hit measure & go to town.
It obviously also does a whole host of other things and provide loads of information about the imported object including simple editing (translating, scaling, mirroring…)
The generate supports also looks useful. (tree supports similar to Cura, but they look more sparse). I need to check this out in more detail.