Gear Junkies: new watch time? HR vs RPE training

Two big questions but related....

Getting back to triathlon after a long time away. I want to train with a better sense of Heart Rate zones to be more effective this time around. I have a garmin 310XT and a heart rate strap. Turns out the HR strap may have crapped the bed, though I do have another better upgraded one around here somewhere that also has bluetooth connection. I used to weigh a whole lot more and I swear the thing couldn't read my heart rate through my fat. No kidding. Now I'm smaller but still big (230ish) and the strap works for 10 minutes on a new battery then dies. Add to this that my 310xt seems to work but has a crack in the screen.

All this plus my gear acquisition syndrome, oh boy...

I also have one of those small fitbit style watches my family got me a couple years ago. I don't worry abotu step counts, but like the HR function. I understand that they may not be very accurate. Sometimes when I know I am working hard it will say I have a pulse of 75. No way. It just seems to miss readings. - Also I don't want to wear it 24/7. It does seem to have a decently accurate GPS, as I will do a run with both and compare. HR (when it appears to work) and GPS are close enough to each other.

So I am figuring maybe it's time to see the latest gear and upgrade it all. But then it also occurs to me that if I already can tell when my HR is up, is RPE a better way to train anyway? Back in the day, all of it was hard, so any exertion was felt as tough. But I'm becoming more aware of my body. I can accurately predict my blood glucose within 10 points usually, and feel like I may be getting close to that with HR.

Still, I know we all love data and I want to collect it if I will actually use it, and if it's reliable.

Any advice?