how do they mix with foundry.
They will mix in fine in both height and bulk with the Foundry Cavalry. The only obvious difference will be the quality of the sculpting. If you are not bothered by that then they will work out just fine.
If I was to chose US cavalry figures today i'd list them in order of preference as Foundry, followed by Artizan and OG last. I bought all the Foundry ones sculpted by Copplestone when they were originally released and still really like them. I think they are spot on for accuracy of equipment etc, but the OG ones do have that Hollywood, yellow neckerchief and braces (suspenders?) look about them.
"Forward Yo!"