I've done VO2 max testing at least 4 different times and I'd have to say that it's always been enlightening. Though once I got used to using my HR zones from the VO2 max testing in conjunction with my HRM, I got a good sense of where my zones are by feel and now I rely on my perceived exertion more than an HRM. Getting the VO2 max done and using that data with the HRM was key for learning that skill.