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Ignore whatever stuff Rulezman is spouting/selling. Don't use a stem for bike fit / reach - that's a roadie thing where they're not turning as much. Stem length has a big affect on steering feel, compounded by bar width, head angle, and trail gradient. Try different conventional ones in the 35-50mm length range and see what feels right to you. If you're sensitive to bike setup, you'll notice even a 2mm difference. In general, if the steering feels too slow, try shorter, and vice versa (too twitchy go longer).

I want to say, buy a bunch of cheap stems and just try it by yourself. Just hoard them (current stash goes from 35mm to 110mm)

I agree with others that 35-50mm is a safe bet, and that the guy in the video you posted is a bit of a kook. I'm running a 60mm stem on my long travel bike, which is clearly "the wrong size," and it's fine. The reach length of the bike is a little shorter than I'd prefer, so I made it feel longer with the long stem. I've got a 40mm stem on my shorter travel bike (because it has a slightly longer reach length than I'd prefer), and it takes roughly zero feet for me to get used to...

You'll end up ordering the one thats in stock and not back ordered. I just installed an i9 35 x 40 on a new build.

Richie rude runs a 50mm, Dan booker a 35mm, average the 2 and you the optimal stem length to ride faster and last longer.

I think the asymmetric thing is way over exaggerated, unless your on some weird old school stem. I generally just pick the stem number than means I can get into an easily repeatable, comfy riding position where I don't have to think to much about weighting. Most of my bikes have shorter 35mmish stems, not for that number as such, because that's what makes the frame reach/stack/bar rise and sweep work.

Run whatever the fast guys run. Don't listen to some guy who sells stems.

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