I use the Blair brand and put a few drops of oil on the spotweld. Be careful with how much pressure you put on them or the teeth will break like glass.
The Blair definitely work better than the HF type but the HF will work if you are methodical. But no matter what you use, slow speed and consistent pressure is key to getting good results. If it starts walking around you risk chipping teeth even on the Blair. Oil helps. Pilot hole or "dimple" is key for cheap ones. I found my Blair will usually work with a good sharp center punch mark. If it starts to walk I partially drill a pilot. I have one of the stepped drill bit type but really haven't tried it yet, but there are multiple opportunities upcoming.
