I like Kaiser personally. But I'm OR. Most other specialties have to float, up to every four hours. That is tough, especially for a new traveler so many travelers hate them. Pay is good so I'd suggest giving it a try.
Kaiser is the largest hospital chain in California. There is zero resume enhancement over any other hospital. Name brands that look impressive on a resume might include hospitals like Duke, UCSF, UCLA, Hopkins, and Stanford. I've worked at those hospitals and other name brand hospitals, and there is nothing about them better than any other teaching hospital, but they do have name recognition so are fun to have on your resume. Even none healthcare professionals will be impressed. But they are not necessary to do well as a traveler. They were not a priority for me, just happened to have a location I wanted to try.
Kaiser has a vendor manager that 99 percent of all contracts go through - American Mobile. Good and bad with vendor managers, but a plus is that they have a uniform contract with Kaiser so other than crisis needs, it is easy to tell what agency really pays the best as they all have the same bill rate. New travelers do OK with American Mobile the agency, but I wouldn't recommend that you work a Kaiser assignment through them. Believe it or not, you are likely to find better money at a subcontracting agency (there are lots of agencies with that contract). An even better reason not to work Kaiser for them is that they may blackball you from working at another agency next time you want to work at Kaiser. Work for a subcontracting agency and you can switch freely.
Everyone has different reasons for everything they do. Joining an organization at a contributing level is no different. Some join PanTravelers to support their mission of educating travelers - tax deductible as a professional organization and a non-profit. Legal help if you have a contract dispute with an agency is like any other type of insurance, a complete waste of money unless you need it. If an article such as the negotiating one or some other tip found there helps increase your pay by as little as one dollar an hour, that is $2,000 a year extra! There is a discount offered for contributing members for the annual Travelers Conference in Las Vegas. PanTravelers is full of unbiased straight truths as they do not accept advertising of any sort, or contributions by agencies. That is pretty valuable when trying to sort through recruiter BS.
My suggestion is to try it for one year. Cheap, and you may have learned enough to not need it after that. You can also get a wealth of information as a free member.