I can only speak as someone who moved to the UK then moved back to the East Coast (considerably closer than California).
First off, it costs a small fortune. As in, probably better to just buy new furniture in California. UNLESS, of course, your friends have an emotional attachment to their things or they are irreplaceable.
I only shipped a couple of pieces if furniture, for the cost I probably could have replaced everything twice over. You also have to consider the wear and tear on the furniture that is shipped.
Second, it takes months, probably not a big issue if they are already settled but a consideration.
Third, get as many estimates as you can, I'm sorry I can't recommend the one I used as they were fairly terrible. They have a cat in their logo. I did a lot of research beforehand but once the bill was paid and the things were packed they could not be bothered to answer my calls. Customer service in the UK is really a joke.