After much research on-line the general consensus is that they have to be installed with grout. They look very much like hard wood and grout will certainly take away that look.
Well I did look you up and saw your site on SM so you're an official contractor. However, as others have noticed, your question is a bit strange for someone that is marketing themselves as a tile contractor.
Let me start with I actually have done exactly what you're asking about so I feel pretty qualified to answer your question. Before that, let's jump back a bit.
Not sure how close Philly is to you but there is a restaurant called Famous Daves that has 3 locations there. They decorate their dining areas with 6" x 24" tiles that your asking about. They use grout. If you can, visit one and get a first hand look at them.
Now, laying tile without grout is highly NOT advisable. The NTCA recommends always using grout. They are actually pushing for large grout joints, not smaller. As man-made tile gets larger and larger, it harder to keep installations flat. Grout joints help diminish the appearance of lippage. I don't care how perfectly flat a subfloor is, you cannot install ceramic tile without lippage. Man-made tile is NEVER perfectly flat.
Now to address my hypocrisy. Yes, I did do a 6" x 24" hardwood look-a-like ceramic install without grout joints. The HO loved it. I got paid. That said, I did have to use
some grout. There was no way, even with rectified tile, to have perfectly butted joints. There also was lippage. I minimized it as much as possible but there was no way to avoid it. The HO actually liked it because they thought it looked more like an old hardwood installation. Whatever. It also took me 2 weeks to do a 20' x 10' area. I will never do it again and I HIGHLY discourage you doing it also. My situation was totally unique and I suppose, I was lucky too.
Do yourself a HUGE favor, don't do the grout-less install. I have no idea what kind of "research" you did but coming from someone who's actually done it, DON'T DO IT.
And tell the dork from DB to go eff himself. :thumbup: