I have had a Black & Decker 4 1/2" grinder for about 20 years. I have used it heavily in my business primarily for grinding welds and cutting bolts.
It still works fine but the transmission is getting loud. I have this tool and a similar vintage B&D abrasive cut-off saw which still works well.
I have had poor luck with the Dewalt version of power tools but I bought a new large B&D buffer which is very powerful and seems solid.
Hope this helps,