If you are doing a large area in them picture yourself setting a solid 12x12 tile level in a bed of peanut butter, fairly easy, press on the entire thing down then put a little more pressure on the high corner or side to set it down. With a sheet of penny tile it is not quite that simple and you have to take more care to get them level. Not at all impossible, just harder. Not sure if they have the slip resistance to make them suitable for floors so check with the seller or check the spec sheet from the manufacturer. Grout space is the biggest issue most people will have with penny tile. There tends to be a bit more grout area. People tend to like to minimize grout because it can mold and attract dirt so keep that in mind for the location of your penny tile.

It's not that tough with the pennyrounds. I've only done one, but it wasn't bad.

I am not sure about keeping thinset from squishing through, but the sheets are "keyed" so they fit together as you lay them. The trick there is to keep the same space between the two sheets as is between the tiles within the sheet. Good luck.

We have googled pics and a pale gray maybe one shade darker than white is our favorite. Anything too much darker than that is more contrasty than we are looking for. The grout color is very prominent with round tiles. I am concerned that white is too much maintenance, but medium gray is too dark. Perhaps we should provide our own grout.