Updated link from https://zeroair.org/2023/08/28/convoy-m21h-flashlight-review/ to https://darrenyeo.com/convoy-m21h-xhp70-3-hi-flashlight-review-best-budget-pocket-rocket/ since the former had some pretty aggressive ads (the new link has some but they were only at the top).
Still has the (sub-)standard Convoy e-switch ui, but the “1%-10%-40%-100%” mode works for me.