I've not used those, but I've used the 1" sq ceramic tiles they sell in 12"x12" pads. [email protected] turned me on to it. You have to remove the glue and backing, but then you are good to go. It took me some time to get it all scrubbed off the back, but I had 144 frag plugs for just a couple dollars and some elbow grease. The ones I used were smooth on the top, so you have to glue to the bottom. It looks like those would allow you to glue on top and bottom. if it's ceramic, you shouldn't have any problems with it in the tank, though.
That is tumbled marble. It is a natural stone(marble/travertine) that is mined from the ground. I would like to say it should be fine to use, but I guess you never know what kind of minerals or metals are inside of stone, so I would go with ceramic.
I am a tile setterr for a living, and ceramic is porous, so it can colonize with bacteria. If you want something like ceramic, but non porous, you can get the porcelaine mosaic tiles.
I have used them many times, the exact same ones that you have pictured and also the tiles that come on a 12X12 sheet that are 1 inch square. I always soaked them in hot water and the mesh will peal off of the back. After that I always boiled them just to make sure nothing was on the tiles that could hurt the reef. You never know what might get spilled onto them, people touching them and so on while in a warehouse or store.
i use the ones that are 12" x 12" with 1" x 1" tiles. I also use the 2" x 2" tiles. I never bothered scraping the backing off. just ripped off the mesh part. No problem with the tanks and I've been using these for about a year...if not more. Hope that helps.
I buy two or three "squares" of the ceramic tiles from Lowes (that Gflat65 mentioned). I pull the gauze off the back and put them in a pot of water and boil them. While they are boiling stir them and they will scrub together and get the paper and glue off. When you think all the paper is off pour off the water and rinse well. You might not have to worry too much about the paper but I've noticed that algae grows on the tiles very easily. I wonder if the remnants of glue is what is fueling the aglae. I butt the tiles togather in the frags trays so close that snails can't get to them. They work just fine and you can have 144 tiles for $6 and change.
Lowes has on sale right now ceramic beige 4x4 tiles. They are not glued and only have the sticker on the back. They will cut for free. I bought 100 tiles for 34. I had them all cut into quarters. Which gave me 400 2x2 tiles! $34 dollars!!