A sight blinder stops the off eye from seeing the bead,; I've used them for 6 years. But it doesn't stop the off eye from seeing the target, which is what I'm trying to focus on in the first place. I agree there's no downside to having one, but it didn't cure my cross-firing. If you want to try a sight blinder, rather than spend $15 for the one pictured, you might buy a $3 set of 20-30 feeler gauges and tape one on the side of the rib rather than on top.
I've shot with both eyes open for 30+ years, during which time I went from occasional cross-firing on very specific target trajectories to unbearable cross-firing on left angles 18 months ago. Since then, I with played with every imaginable "trick" (occlusion) which, in effect, was trying to become a one-eyed shooter. I'm cautiously optimistic that I've cured my cross-dominance and, in that regard, am a better trap shooter than I've ever been ... still with 2 eyes open.