Bought them to drill holes on a quartz counter top. They performed admirably. I drilled about 12 holes with 22mm one and it is still going strong.
Two things to watch out for when you use these bits though.
1. You will need a hole guide unless you are very experienced. They will stay in place after they bite, but in the beginning it is hard to control the drilling position. You can try to solve the problem by going in at an angle but it is not the easiest method. I drilled a larger hole on a piece of scrap wood as a guide.
2. You will need to cool the bits as you drill. I filled my drill guide (that piece of scrap wood with a hole) with water and constantly top it off. The water also prevents any dust from forming and prolongs the life of the bits.

I renovated our kids bath and decided to lay 12" porcelain wall tile around the perimeter of the bathroom and in the tower surround. Porcelain tile is really tough to cut. The bath has two sinks, john, and tub/shower. Plus towel bars, etc. All these needed holes drilled through the tile. I bought some diamond drill bits at lowes, which all broke on me. They were danged expensive. The problem is I have a variety of sized holes to drill for 1/2 & 3/4 pipe, 1/8 OD pipe, screw holes, etc. I decided to give these a shot given the price. I am really glad that I did. This bit just kept on going. Nice clean cuts (see photo). The key was to keep the drill on a relatively slow speed and use a spray bottle to keep it wet. I had 7 holes to drill for 1/2 pipe (Actually had to drill 9 b/c of two miss measurements :-)). Each takes a few minutes to cut through the porcelain (which is even tough to cut with my tile saw with a diamond blade). But, it gave a nice clean cut. Granted, I am a do-it your-selfer - not a pro. I have another bath to renovate. I'll be able to use this bit set to get that done as well. Then I let them rest, hopefully for a long time!

I Needed these bits for drilling holes through ceramic tile/concrete backer board to mount a glass shower stall. I was able to drill about 12 holes with the smaller 8 mm with no problems, however the bit is almost worn out -- which actually exceeded my expectations. I also used the largest bit to cut out a 3" x 3" hole with multiple passes in the middle of a tile to fit the shower handle.

These bits have no center pilot bit. I've found the best way to center the bit to get it started using a thin piece of wood with a hole the size of the bit in it and then position the hole in the wood right over my mark. Perfectly positions the bit and prevents drift when getting started.

Use a wet towel to keep the tile and bit wet with water. Stop often to wipe the bit with the wet towel to keep it cool. Otherwise, like any bit, it will fail quickly.

Cannot beat these for the price! Used them to complete tile upgrade to tub and shower surround. Without these the job would have been impossible. Used several of the enclosed sizes and all worked to perfection; a couple of them were used multiple times and remained sharp enough to easily cut through large / thick porcelain tiles. The variety of sizes were very useful, allowing us to complete the job without any of those "oh no!" moments that so often happen during DIY projects.

. FINALLY SOMETHING THAT WORKS! I've been looking for something to drill holes in liquor bottles for lamps & misc. I've been talking to people at Lowes & Home Depot for *months*. Not once has anyone recommended these. I scoured Youtube videos & finally found a tutorial that demonstrated exactly what they have succinctly done with their step by step drawing. Not only do they work as described but you receive all of the sizes for this low price. That being said, I've only been using them for 2 months and I have *always* used a reservoir filled with water while drilling (use plumber's putty, roll it out and then join together and seal a "wall" around where you want to drill. With the *plumber's* putty it will hold water until you get through the glass, obviously the water will go through your hole so you made need to safely (if you're not using a cordless) have some water poured onto your hole as you finish drilling) & I've only been drilling liquor or wine bottles thus far. If they break on me...I'll update this but I have to say for the price compared to other drill bits I'd have to take that into consideration.