I also have not used them. I did see a poster wanting to replace his because they stain easily - he had glass ring marks and stains from oils. I don't know if there is a way to prevent that - some consider it "patina", others just messy looking.

There have been some good stories here about what they're like, pros and cons, etc:

https://www.houzz.com/ideabooks/query/concrete-counters

just had these installed. Our previous countertops in another bath and the kitchen were concrete. They were great for 17 years, but got tired of them. They did eventually stain, but I never resealed them. Apparently the newer sealers are better so we'll see!

Anyone interested in concrete countertops should give the new Cantera from Livingstone a look. Superior to concrete in every way.

Cantera might be the way to go as Joseph Corlett mentions. My understanding is they are very prone to staining. I do love them and would go that route one day not too far off when I build again. However, I'm scared to do so from a friends experience. Weedmeyer obviously had a job done well.... I'm not a fan of high shine concrete counters, but I think that is the only way to get them to be a lot less porous and maybe weedmeyer knows more about this.

I took that picture after the guy had just applied the sealer. It is already more matte as I had told him I don't like high gloss either. It is in a bathroom that will be used in my craft room, so we'll see about staining. He looked at my old countertops and assured me that sealers have come a long way since I originally did the other ones 17 years ago, but time will tell.

That Cantera will take a nice matte finish.

Look around online. Lots of solid surface manufacturers have concrete look-alikes. You have to see the material in person. Livingstone and others send samples for free.