A Hair transplant is not a Pepsi i.e the same thing in different stores. It is very dependent on the method and approach to the procedure. You can get people that do everything right, or those that do everything wrong. So many variables exist in a hair transplant that it is good to first do a lot of research on the place you want doing your transplant.
A hair transplant is a hair transplant no matter what country you are in.The techniques for this are well defined and the doctors hopefully will follow the Standard of Care no matter what country they are in. We have an International society (ISHRS) where doctors from all over the world come and share their experiences. If anyone has a 'better mousetrap' they can present it at the annual meeting and publish it in medical journals as it is the responsibility for every doctor to educate their colleagues. So to answer your questions, a Hair Transplant in the US should be identical to a hair transplant in Mexico. What differentiates the two may be the experience and the skill of the doctors and their surgical team. The techniques must all fall within the Standard of Care and that is a world-wide standard.