The brightening effect of yellow is largely perceived. It's about contrast. In low light contrast naturally decreases. Yellow adds contrast, hence making it seem "brighter".
But it's not really brighter. If you have amber, gray, and yellow lenses all with exactly the same light transmission, and keep them all on until you HAVE to take them off to be able to see anything, you will take them all off at the same time.
So, if "how low can you go" is the primary concern, it's all about light transmission. It's true that yellow lenses often have higher transmission, because they were designed for low light. Correlation, not causation. But theoretically the highest transmission you can get in a polarizer is a light gray. i.e. JUST the polarizer, nothing else. A polarizer, by definition, blocks 50% of the light of neutral color (gray). No contrast enhancement. Any tint on top of that is blocking light, even if it's yellow.
My take in a low light lens is that, on that May evening where you're staying out after dark, I don't really care if I gotta take it off at 8:50 vs. 8:55 as light fades fast, but I don't wanna have to take it off at 7:00, or in daytime on those cloudy drizzly days or under a thick hemlock canopy. And I'll take contrast enhancement in merely dim environs over an extra 5 minutes in truly dark ones. Make my low light lens a cool yellow, thank you. I like my MJ's, and would probably like others as well.
As such, I'd probably agree with Idrather in not preferring the Smith's, even though they are technically the lowest light lens of all and likely well polarized. Smith makes some good stuff. I just don't think those are for me.....