"I should probably have mentioned my edge is just a basic eased edge."

Than just about anything is an 'upgrade' since it takes more work.

Mitered edges reduce the appearance of a thicker counter.

Sort of the opposite of what was done by laminating.

In my mind, a mitered edge is just that -- a miter rather than a butt joint. What you have now is just a rectangular piece of marble stuck to the bottom of your contertop. With the miter, they will cut back the edge of your counter at about 45 degrees. Then the piece that creates the built-up edge will also be cut to match that 45 degrees, and be attached. The seam will be the edge of the countertop itself -- not a visible seam along the middle of the edge piece. Now, color match is still an issue, but a mismatch won't be as obvious. If they used a piece from the same lot as the previous piece, you would see the darker top of your counter, and the white on the side -- still a mismatch, but not as obvious that it is two different pieces. I think it would probably look as though, when "sliced" the marble was dark on the outside and white on the inside. They still need to look for a better match.

When we got our countertops made a few years ago, my fabricator refused to do mitered edges on my connemara marble.

Given that the stone was very expensive, and he had never handled it, he would not take the liability of cracking the slab (there are many many fissures) or the 45 deg miter (edges can chip easier).

In the end we went with a flat built up edge. I am pretty happy with it. The joint is seamless. The laminated piece continues the figure of the stone. A miter would have been nicer but I did not want to risk buying more slabs. I did supervise the cutting of the stone and it cuts easily. So a miter would have been not any riskier but the fabricator was over cautious ;)

how think is your countertop?

how thick is the raw slab?

yes, a miterd edge is harder to fabricate and is more costly.

without seeing your answers yet, I can confirm that the proposed work is real work that has to be paid for, so I think they definitely are doing you a favor. I'll guess your countertop is 3 cm thick.

I did a mitred edge on my quartz/caesarstone counter and didn't pay any additional for it. I was doing white and had seen some really bad jobs that had visible laminated edge seams when it wasn't mitred. They're usually able to hide the seam with darker colors or slabs that have a lot of movement, but with light colors mitring us the way to go in my opinion.

Thanks everyone for your responses so far. I will add what detail I can.

I am on the west coast so my slabs are 2cm. I will still have a built up edge with the mitered sides.

They say that they found the rest if my slab and will use it to fabricate. I td them I will not accept a badly matched edge. They tell me the wrong piece was used before which is why it didn't match. No clue if this is true but they will be doing it over again if it doesn't match well.

They are their slabs, so if they ruin during fabrication they replace. it's a low budget remodel so I took what looked good and was reasonably priced. The place does have a reputation for quality work.

They are telling me that it will now be virtually unnoticeable. Their other seams look great so I have no doubt that they can pull it off, I just want to be sure it is in my best interest as they say.