They work OK.....although you DO need to drill slow....150 rpm's or so and keep the hole wet. Use a wet sponge or sprayer for this.

Set the bit at an extreme angle to establish a "dish" to gradually lift the bit up to.....otherwise it will "walk" all over the place.....

We bought a similar set off of Amazon, but the saws are larger in diameter. While they are a bit hard to use, DH said they do work (used on both porcelain and limestone tiles) and so far he's happy with the purchase.

I used to sometimes take a roughly 4" square of 1/2" thick scrap plywood, drill a hole through it that's the diameter of the bit, then put the hole in the ply over the spot where I wanted to drill the hole through the tile/glass/stone.

Hold the ply in place with one hand, drill with the other. Once the hole is started you can remove the ply and use the free hand to squirt water.

If drilling on the flat, you can keep the ply in place and use it as a dam to contain the water.

Dont make your first hole full size. Start with a smaller bit and work your way up.

I really appreciate getting comments from the experts. Please don't mind my additional questions...yes, I was that kid that always had my hand up!

So Mongoct, what does using the plywood do? I can see it holding water when flat on the floor, but what is the purpose of using it to start the hole?

Tim, why start with a smaller bit? Would you use a diamond hole saw in the smaller size too?

raehelen-
If you don't use a guide of some kind, like the plywood jig mongo describes, the bit will jump all over the place and deface the surface where you don't want it to. Trust me, you can't hold a bit like that in one place by hand once the drill starts up.

As for starting with a smaller hole, this is often done with hard materials. It takes relatively little effort to make a small hole, and then work up to full size, whereas trying to make a big hole with one bit can be harder and take longer.

Below is a video from a company that makes a high end drill bit system for porcelain tile. At about the one-and-one-half minute mark you can see why a jig of some kind is useful for the kind of drilling you want to do.

Here is a link that might be useful: Porcelain tile drilling

Kudzu, that was a great video. He explained how to drill very well. We've been using a spray bottle, I think we'll try a sponge next time. I'm going to have to pass kudos on to my DH who has drilled about a dozen holes so far in the porcelain tiles for this reno with no guides and the holes all look perfect, though he does complain about how frikken hard the porcelain is to cut through! LOL

I still don't quite understand the purpose of the smaller hole though, as the hole saw would miss the smaller hole, seems to me it's just twice the work?

raehelen-
Regarding the smaller hole...you're right as far as using the type of bit you have. That description mainly applies to steel or to using a different type of bit on porcelain.
By the way, are you using your eBay bits? If they're any good, I might get a set.

Kudzu, I just ordered them on Sunday. They're coming from China or Hong Kong, (I don't remember which). All we have left to install are the grab bars, and an extra hook for the hand shower, so we're going to wait until the bits get here to try them out. Will definitely report back and pass on the seller's name. There are several that sell these bits, this was the cheapest.

I've had mixed success ordering cheap knock-offs from eBay. eg. One set of phone batteries (which here would be ~$25) were $1.99 each with free shipping and no tax. I've had them for several years and they are fine. Batteries for another set of cordless phones (Unfortunately the first seller didn't sell that type), and they don't work at all. At 66 cents each for diamond coated bits compared to $16 + 12%tax, I couldn't afford not to try! LOL

Thanks. I went to the link you provided in your initial post and it looks like the seller has a very high rating, so I hope the bits turn out to be good quality.