Not flat-bar levers to fit a drop bar, and not a 'how to' post at all (probably doesn't belong in The Knowledge but wasn't sure where to put it; not Reviews cos I haven't used or even seen it). This is a drop bar designed to be compatible with mountain bike levers and shifters.
It's kind of like a wide, shallow drop bar might be with the bar ends of a flat bar stuck on the hoods, and all made of flat-bar size tubing. So it's for converting a mtb to drops not a road bike to flat bars. In fact it's got a 25.4mm clamp diameter so won't fit most modern stems whether they're road or mountain. And because it's steel, it weighs over 700g (it's suggested that because it involves welds, aluminium might not pass strength tests).
I'm not entirely convinced by it, but then I'm not a mountain biker or even a gravel biker (I do own something that might be considered a gravel bike but the use I put it to is definitely more surfaced – it even has a pannier rack!). There's a comment comparing it to an upside down North Road bar, and I tend to think in that situation I'd prefer a North Road bar (but the right way up). And lastly, I note there's no price mentioned.
https://bikepacking.com/gear/surly-corner-bar-review/Anyway, I await the forum's appraisal.