They work well if used carefully. I've drilled a few holes in solid concrete and brick and they're holding up well. To get the most out of them, there are a few tips to keep in mind, but not all of them were good. The body is quite flimsy and probably won't last long, and the foam insert is cut too deep for the middle bits and shanks, making them difficult to remove. The bolt that holds the center drill in the shank does not last long: after about a minute of hammer drilling, it falls out and the center drill gets stuck in the workpiece. A few tips for more convenient use: 1.) Pre-drill the center pilot hole separately to reduce the stress on the center nozzle stop bolt. 2.) Use these hole saws to make shallow (1/8 inch) grooves in the surface of the work piece. Then use a small concrete drill to drill a series of small holes in the newly created groove (around the perimeter where the hole will be) all the way through the piece. Then come back with a crown and finish the last drill. 3.) For larger drills, drill a little slower and take enough breaks to allow the drill to cool. 4.) Be sure to use the hammer feature for best performance. 5.) Remove core material frequently (about every 1 inch depth) to prevent sticking