I hope this doesn't launch a flamewar....
I just had a quick look at the NAR and Tripoli pages; looks like membership is $60-70 a year. I get that I need a membership to get HPR certified (though I'm quite certain that having fun with MPR will last me for some time).
...Apart from the certification opportunities, the magazine, and the liability insurance (which, if I'm launching with a local club, I should be covered, I think) .... is there a reason for someone noodling around with LPR and MPR to get a membership? If so, which one?
I belong to both. Your membership will be a small fraction of what you spend in a year and the benefits far exceeds the costs.
Only NAR or TRA members have personal liability coverage at either groups launches. You as a flyer have none, and in the worst case scenario you still could be sued individually if you were a launch participant (launched a rocket) and all launch participants were sued, even though you had nothing to do with the property damage or injury. For personal protection you could add an umbrella polity to you house and car insurance, but you will have to maximize those policies first and then pay an additional several hundred dollars to get a $2M umbrella policy....which is going to be at least 5 times the cost of NAR or TRA dues......
TRA Prefectures have no insurance coverage for uninsured participants so if you have an accident so they should require you to have either TRA or NAR membership.
NAR Sections are protected if a person who is not a member of NAR or TRA launch a model rocket that causes damage. If it was a high power rocket, it would be a violation of the NAR safety code which requires high power certification which is only valid if you are a member of NAR or TRA.
Both NAR and TRA offer a $5,000,000 primary liability insurance policy for they members. The NAR pays about $50K-S60K for their insurance policy. With ~6,000 members, that's about $10 per member, or about 16% of the NAR dues (the magazine and other publications accounts for slightly more than 50% or ~$32 per member. TRA pays ~$110K for their insurance policy. With ~3,800 members, that's about $30 per member, or about half of the $60 annual dues. (Numbers are complied from a number of sources without going back and verifying them for currency.)
TRA insurance covers your minor children, NAR's does not. TRA insurance is world-wide, NAR covers you activities in the US and Canada.
The bottom line is that it is to your advantage to join whichever organization that you local club is affiliated with. $60 which is about $1.20 per week is a cheap premium for a $5,000,000 liability policy.
Bob