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.

We encountered something similiar with about a 2" on the end of one wall, however we were going with the tile vertical and stacked above one another. We had a professional, who laid our tile in the majority of our house come over to answer a question we had about the window in the shower and before Hubs could even ask him about that, he looked at Hubs layout and said, "you never have that small of tile on the end of a wall." That and the issue of the window had us re evaluating everything. He wanted us to bricklay the tile (12x24, like yours with 1/8 grout line), as he said that was the way to solve any issues. That wasn't the look I wanted so we started over and Hubs, with the help of some people on here, finally came up with a solution. We ended up going horizontal but matching grout lines. Before any tile is laid though, make sure your tile is actually 12x24. Ours was actually a little less than 12 and a little less than 24. That little bit adds up when you only want 1/8" grout line and you are dealing with a small bit on the end of a wall. I didn't want bricklay pattern as I wanted a flow from the floor to the shower since we are having a 39" glass panel and 30" glass door. So far, it has taken hubs a couple of weeks to cut and lay the tile himself, but all the grout lines are even and we are down to finishing the bullnose and the floor. If you are wanting the bricklay pattern, then your tile guy's solution might work. Try drawing it out on the computer and see what it looks like. That's what Hubs did and it helped me see what he was wanting to do, or draw it out on the shower wall itself.

Attaching picture of 12x24 tile. Note the patten repeated every 3 rows. Going in the same direction of wood floor in other room (long way of kitchen). Note 3rd picture showing hall. If you put the short way of the room look at the cuts. Will you have a lot of cuts those lose the reason for the 12x24 tile. I think if you want see 5 or more or more full tiles per row why do the 12x24 Below is example of how it looks in the hall

Laying the tile vertical can make the room look taller while going horizontal can make it look wider (similar to the vertical vs horizontal stripes on clothes). I think it also gives a more modern feel. We went vertical with the 12 x 24" tile in our shower. Our house tends toward mid-century modern so the modern feel goes with the bones of the house. Part of the reason that we chose vertical is the tiled bench in the shower. By going vertical with the tiles, there are only vertical grout lines on the bench since the 24" direction of a tile is longer than the the height of the bench and longer than the depth of the bench. If we had used the horizontal direction, there would have been horizontal and vertical grout lines on the bench side and top as well as vertical ones. There are two ways to do a 1/3 stagger. In one, you move the tile edge 1/3 of a tile in the same direction for each row so you have 3 kinds of row. E.g. if you move to the left each time and start the first row with a full tile, the next row with 2/3 of a tile and the row after with 1/3 of a tile, then the next row you are back to a full tile. The other way is to use only 2 kinds of row so the rows alternate by moving over by 1/3 of a tile and then back the other direction by 1/3 of a tile. E.g. if the first row started with a full tile, the next row started with 2/3 of a tile and the row started with a full tile. I guess one could see the grout lines in the first way as looking like steps of a stair. Personally, I prefer the look with 3 rows of the pattern over the look with two rows. I don't see why one is "wrong" and the other "right". Seems like personal preference in which pattern is preferred.