I purchased both the Dremel 569 and 570 carbide grout removal bits to perform what I thought would be a fairly straightforward removal of old grout from our bathtub tiling. The bits work very well for about 15 minutes (i.e., about 7-8 linear feet of grout) and then go dull to the point that the bit refuses to cut anymore and the tip glows red hot even with slight pressure. I am now on my 14th bit and I still have about 15 feet of grout to remove. Given that these bits sell for between $11 and $15, this is a ridiculously short bit life for what is relatively soft gypsum material; it's not like I'm trying to cut through concrete or sheet metal. I've tried every possible technique, including cooling the bit down for a minute after each foot of grout removal, but nothing extended the life of the bit by much. Moreover, although I'm not a professional contractor, I have about three decades of experience with power tools, so I'm pretty confident I'm not using the bits in a manner that would be outside their performance scope. Dremel really needs to either drop the price of these bits to a couple of bucks and bundle them by the dozen, or upgrade the quality so that it actually is worth the current asking price. No one should have to pay close to $200 in grout removal bits for a simple, straightforward residential bathroom grouting job.