I have used several in California including the big center at the Oakland Temple, and am a volunteer at the one closest to me (I am not LDS). No one will give you a religious pitch, and you will not get a visit from the missionaries. The FHC centers are very inviting, the volunteers will try to help with what ever you ask for. If you do not need help, you are free to work on your own.
My local FHC Center has a good relationship with the Livermore Amador Genealogical Society and over the years have jointly sponsored a number genealogical events for the public.
It is a great place to work, and I am grateful for the resources they have made available without cost to all of us.