None of this is scientifically verified, but:
The different National versions are more or less dense formulations of Seamoon with a dye. The order should be something like Black > White > Yellow > Seamoon. I don't know where Red, Brown, 2017 or any other obscure versions fall.
The peak effect lasts a day or two or so, then a stable high effect for 1 to 2 weeks (Haifu claims +8.5% for 1 week for Black), then drop off to nothing after about 3 to 4 weeks.
They all soften the sponge maximally as much (Maxing out at around 9deg softening for many sponges I've boosted 4-6 times to see where it reaches asymptote) although the stronger national boosters soften it faster, and denser sponges soften more per layer.
Black softens the sponge the easiest and Seamoon the hardest. However you need less of Black to get a similar elasticity effect as with Seamoon, so maybe there's a breakpoint where you get more elasticity than you get softening. I have no clue where the idea that Black softens the sponge less comes from; I find on average 1deg more per layer (2ml or so) than with Seamoon.
I've found on less dense sponges with Seamoon it can be as little as 1deg per layer, while on dense sponges with Black it can be as much as 3deg per layer.
In practical use I haven't noticed a real difference other than National boosters are stronger so you can get less added racket mass for the same softening and elasticity. Black and White are a lot stickier and much harder to evenly apply than Seamoon, and harder to drain back into the bottle. I haven't tried Yellow but under spectrometry it's identical to Seamoon so it's probably just a denser variant as well.