I use to be of the "old school" when it came to grinding welds, using a hard solid wheel, but flap discs have evolved quite a bit in the last decade or so, there's angled discs, flat discs, even discs just for doing 90 degree joints, "see thru" flap discs so you can see exactly what your grinding under the disc as it's cutting, "cool run" flap discs, etc, etc, the down side is price, most are $10-$20 each and don't last long, so most stick with the $3-$4 hard grinding wheels/disc, once you use a proper flap wheel for cutting down and finishing a weld, you'll never use a black hard disc ever again, the only time I find myself needing a hard disc is to cut down a grotesque weld one of the new guys welding at the shop may have done, just so I don't waste a good flap wheel....but to each his/her own, as we learn and like different styles/techniques, but it's always good to hear/see others experiences

Mike