Very good hole-saws, and this kit is by far the most complete I have ever seen.  A really good price for this many different sizes.  I have used these  in hardwoods with good results, just remember to back it off often and clean the shavings out of the teeth.  If you don't it will start to burn and the heat will shorten the life of the teeth as it anneals the steel. The slots on the sides are great for prying out wood plugs with a flat-blade screwdriver.  I have also used these hole-saws to cut holes in heavy gauge steel electrical junction boxes without any problems.  They remain sharp and last for many cuts.  Very important! Always drill your pilot hole through sheet metal before you put the hole saw on the arbor!  Otherwise you will have bent or broken pilot bits and missing teeth on your hole saw (I was an apprentice once and I know this for a fact!).  This is not the first Lenox set I have bought and I keep buying them for a reason.  I have used Milwaukee, Greenlee, Ridgid, and other quality brands of hole-saws.  Lenox is at least as good a anyone out there in this price range.