I think I'd benefit from having an HRM and such.. probably proper speed and cadence too
I'm really just at the start of my "fitness journey" though. I can handle longer rides, climbs and sustained riding but not at anything like the sustained speed the more pro cyclists (on here) regularly do.
I personally just want a speed sensor so I know exactly what my avg etc speeds were

garmin loves to freak out in london for no reason.. and going 20mph shows 7mph then jumps to 38mph and so on..