Depends on the woman. Some don't mind as long as everyone knows their place. She's the wife. She's the one with the major assets coming to her. The mia noi is financially supported but she has no rights (or expectations) of inheriting any wealth from the man. The gik is simply someone who is available for sex in exchange for either cash or gifts.

It's not entirely unheard of for the mia noi to live with the husband and wife. Not common but I've seen it in enough Thai soap operas where it can't be completely uncommon either. Again, as long as the mia noi knows her place, the first wife often is glad to have someone to hand off her house duties to.