i've been a navhda member for ten years or so, and have nothing but good things to say about the organization. I've tested five dogs in na, and took one through the ut and the invitational.
The tests obviously include a component of luck, but by and large they do a nice job of helping you find out if there are holes in your dog's performance or ability. I always enjoy having my dog, and my training ability, evaluated by a group of judges who have likely forgotten more about bird dogs than i'll ever know.
Na tests seem to be the least accurate in terms of measuring a dog, as there's a big range in the ages of pups tested, and it's easier for a young dog to have an off day and blow the test. I wouldn't get too discouraged about a disappointing na score, as that same pup might ace everything if it were to be tested again the next day.
The ut is pretty challenging, as the dog is asked to perform a wide variety of tasks and the bar is set fairly high. You're working with a more mature dog, and should be able to expect a little more consistency than you would from an na pup. If you get a dog through the ut, you'll have a pretty well-behaved hunting companion.
The invitational is really nerve-wracking, as you've spent a lot of time and a fair amount of cash (chukars / pigeons / ducks / shells / gas / lodging / etc) to get there, and the pressure is pretty high. You pull into the test and see rigs from all over the us and canada, and it hits you that this is a really big deal. Your dog has to show a lot of prey drive along with pretty impeccable manners, and it's very easy for the wheels to come off at some point during the day. I put in a lot of work in getting ready for that test, but the satisfaction of hearing the judges say "...and new versatile champion....." at the end of the day was an incredible reward. I left that test with a pointer that can nail blind and double-marked retrieves, is steady and quiet in a duck blind, backs reliably, is consistently obedient, and can really tear things up in the field.
Best part of navhda is the friends you'll make, and the knowledge they'll share with you. I had several very experienced and talented handlers open their homes to me to help me train for the invitational, and was able to pick up tips from those guys that would have taken me years to learn from books or videos. I'm 400 miles away from my chapter, so i usually can't take advantage or training days or seminars , but i can pick up the phone at any time, call some of the veterans, and get an enthusiastic and valuable answer to whatever questions i might have. Navhda is great in the sense that most everyone pulls for each other. You'll probably run into another handler or two along the way who wouldn't be your first choice for a hunting companion, but by and large you'll encounter like-minded folks who will often become good friends. I have a whole new set of folks to train and hunt with as a result of my involvement.
Get signed up with the organization, jump into a training day or attend a test or two to get a feel for what it's all about, and chances are you and your dog will have great experiences.