I call BS. Throws everything this person has said and done so far into question.

Well, I really have any tiling expertise except what I've learned here. The picture you posted (blue tile) has visible grout lines. The tile is beautiful & if this is the look you are going for, maybe no visible grout lines isn't what you want. How does grout lines versus no grout lines effect lipping/lippage?
Just trying to figure out why it's an upgrade.

" But I am worried about small gaps and about kitchen grease/moisture entering. Should I be?"

I would be, but I'm a function over form kinda guy when it comes to sanitation. Especially common sense sanitation.

When I ordered my bs tile and was choosing grout the guy said, and rightly so, that if I matched the grout perfectly to the tile I would totally lose the effect of the running bond layout. Since he was absolutely right I went with a non-matching but lightly complementary color instead.

I know grout color is mot your issue here but the concept is the same. You will lose nearly all definition without the right grout lines, as evidenced in the picture of your tiles above. It will become a veritable ocean of solid blue.

So, unless that is the look you are going for, consider it carefully.

1/16" is usually the smallest recommended. With irregular tiles, you might want to see how they lay out that close. Wider joints handle irregularities and lippage issues when the tiles don't lay flat.

I believe I've read on John Bridge that there has to be a joint in order for the grout to bond and stay in. Do your own research to be safe.

I think the Fireclay fireplace photo, linked in your original post, is an optical illusion. The head on photo, linked below, clearly has a visible grout line.

Here is a link that might be useful: [Fireclay vitrail fireplace surround[(https://www.houzz.com/photos/san-francisco-victorian-contemporary-family-room-san-francisco-phvw-vp~1710647)

I think that technique would not look very good with a tile like Fireclay since these tiles are not perfectly even. There will be parts of the tile that are not plane to the surface and without grout you might be able to see the unglazed portion of the tile sticking up. It would look very "rustic" and I am sure that is not the look you are trying to achieve.

The only time I have ever heard of that technique being viable is with rectified tile and even with rectified installers still like to leave about 1/16" for the grout.

Thanks everyone for confirming my suspicions - we'll go with grout! Greenhaven, good tip on the grout color, too. If GC supplies any reasonable justification for why this counts as an 'upgrade' I will keep you posted, for entertainment's sake if nothing else.

There are standards for tile setting which require an average grout line of 2x the maximum variation in the size of the tile. If the tile varies 1/16th" from tile to tile, then the average grout line should be 1/8". I don't see how tile that varies in size can be close set without a visible grout line.

There are tiles made to be butted. These are "rectified" tiles and are cut with a saw or grinder to be exactly the same size. But, it does not sound like these are the tile you have.