Is it visible to anyone standing in the kitchen? Is it only visible when you're working on something? How much is it going to bug you over the course of the next 5 years or so?

If you can say "aw screw it" and ignore it, there's your answer. If it's visible and you can't park the coffee maker or food processor in front of it and it's going to make you annoyed at the contractor every time you see it, then get it replaced.

As for where the tile starts, it was six of one and half a dozen of the other. I agree with the contractor that it would look weirder if it missed the last inch of the countertop but YMMV. It was going to be off kilter no matter what he did. What you can do is get some milled lumber, stain it to match the cabinet, and tack it up so everything looks more even. Some fixes are cheap and dirty, this one is.

replace it versus live with it. If it's easy to replace, then I'd like it done.

Thanks for the info about where to start the backsplash

Are there any whole pieces of tile from the original batch left? On things like aluminum, and particularly brushed aluminum, any replaced pieces often stand out more glaringly than a small dent. Our eyes will always look at the largest imperfection first; fix that and then there is another largest imperfection. Being this is special and familiar to you (I don't mean this negatively), you will see details that no one else will notice. Guys in trades like this might tell you to squint your eyes when you look at it because that is closer to how others will see it.

As far as where the tiles line up and where they started - not enough information. It is normal to start with a whole tile at a corner and then work toward the open end, finishing with a bullnosed piece or cap of some type.

which I'm going to rectify because I paid for them. Thanks for the info

a few years down the road.

The installer must have taken them, I'll rectify that tomorrow.

Thank you!

otherwise I would always "see" it and regret I didn't do something about it. Who cares if they think you are picky?

I have too many stories of where I wish I had been more picky.

and they're coming back.

Thanks for all the advice