So I recently built a MTB (fits into the downcountry slot) and wasn't sure about size. It was my first proper MTB so didn't have experience to rely on, picked a large frame based on other's heights & inseams, and what they thought of their fit. When I built the bike up the distance from bars to saddle seemed ridiulously small. I thought I'd made a big mistake. After riding it a bit and making little tweaks to stem and types of handle bar the bike feels soooo good. It wasn't until later, going down the youtube rabbit hole, that I came across the RAD fit method. For curiosity I measured it up and turns out the RAD is pretty much bang on (IIRC within 1cm). I know it's only a sample size of one, but seems there's something to it.