Although it looks intricate as hell, the herringbone is very simply, a brick joint pattern with every other tile turned on its side. Look at the pattern for a minute. You'll see that first the horizontal tiles look like steps, with each step being exactly a 1/2 tile advanced from the last. Then comes the vertical tiles doing the same thing. Then back to the horizontal tiles, and so on. Once you get going with it, it's really not as complicated as it looks. The only disadvantage is that your grout joint is predetermined by the tile size. If you lay two tiles longways side by side right next to a single tile cappling the ends of the two tiles, move the first two so their long edge is flush with either end of the capping tile. Whatever you have for a joint between the two tiles is what you're going to use for a grout joint throughout the floor. No ifs, ands, or buts.

Geez, now I've something else to think about! Still haven't decided what we're doing in the two upstairs bathrooms, but really like lanugget's and kitchenkelly's tiles! (And bonus of large tiles, is that there's less grout!)

You can check flatness by taking a pair of tiles and placing them face to face or back to back. If there is any gapping around the edges or in the center when you look at them from the side, then they are not perfectly flat. That doesn't mean that they can't be used. It just means that they will look better if they are not laid in an overlapping pattern where you get lippage, and it is important, if they are bowed, that it is consistent from tile to tile. I did a small bathroom in 18" square tiles that were perfectly flat and I still chose to align the tiles in a standard, straight set pattern. Lippage

I‘lol comment on the “quality” aspect a little. My previous house had tile throughout the main living areas and it was laid on the diagonal. Initially when we looked at (&bought) the house we too thought it was different/special/unique/whatever. Friends commented on it looking nice. However, it just really sucked. Rugs and furniture placement always looked bad bc it was hard to get them lined up with the angle or exactly perpendicular to it. It quickly became a PIA. It never just blended away as a floor. I know yours is a bathroom but I would still rethink it. It could easily end up looking like you just couldn’t make a straight line. Maybe use a smaller rectangle tile for herringbone or another interesting layout or find some interesting tile and do a stacked or offset pattern. I think you’d find it nicer and less “unique”. Sometimes unique is the equivalent of bless your heart.