Well, a little bigger than true mosaics. 2x2. I thought it might be neater to run a bead of the epoxy grout. The website of the company that sells the gun shows it filling what looks to be a 1/8" grout joint.
I use one that attaches to a drill. works great. Use it for tiles, stone work. Bought it originally for a job that needed 85,000 sq ft of brick. One of my union bricklayers wanted it. Used 4 of them. Cleans easily and less wasted materials and less cleanup.