Agree that it's not needed, but it can be a useful tool and not necessarily just for someone with years in the sport. I didn't get a power meter until about 18 months ago when I started working with a coach who preferred to use power-based plans, but actually in my first years of tri, before I got a bike trainer, I was doing most of my harder cycling workouts on gym stationaries with watt meters
(while not terribly accurate, they do provide some kind of metric that is consistent between workouts
) and using power-based plans here on BT. I have a strong run and swim background and good sense of pace/effort for those sports, but not so much for cycling--my only background had been casual touring and commuting. I found power to be really helpful in structuring workouts and giving me a sense of how I was progressing; also think had I gotten one for my bike and learned how to use it sooner, I might have avoided some of the overtraining, gearing, cadence, and pacing mistakes I was making in my first few years that made the bike, and sometimes the run, tougher than it needed to be. For two years after I got the trainer, I trained by HR, but that can be difficult to use to structure workouts outdoors with variable terrain and weather. I was glad to return to training with power after getting the PM and feel it has been a worthwhile investment both for training and racing.
It sounds like you are already quite a strong athlete, especially on the bike. I would educate yourself on the use of the PM in training and racing, and, if you are still interested, find a model that fits your needs and budget. They need not cost as much as the bike. I think I got mine on a Black Friday special that, bundled with a Garmin bike computer, cost about $600. There are cheaper
(but possibly less accurate models
), also ones that are much higher-end. But no, not a necessity, especially for a relative beginner.