Strava

how accurate is Strava?

Eh, at what?

It's as accurate as GPS is, so plenty good enough for cycling assuming the ride/segments are of a minimum length (let's say 500m). It's less accurate in urban areas but that's just GPS sucking, not Strava. The calorie count is actually pretty scarily on hills in my experience, less so on flats especially if you are drafting (hello Regents Park chaingangs).

Is it accurate at telling you how good you are? Depends. You have to ignore famous segments (Box Hill, anything Richmond/Regents) as they have the obvious cheats as well as authentic attempts by pros, chaingangs, "white van" motorpacers, TT bikes, etc etc. The solution, like a lot of things in life, is to compare yourself with your past self rather than others..