That doesn't make much sense. If the "sloshing action" dampened recoil, why not just fill the guide rod with water?
You could, but mercury is much denser and takes up less space, transfers greater momentum. I've used a mercury recoil damper in my shotgun and it was effective in what it's for.
It
doesn't reduce recoil, it
spreads the recoil energy over extra milliseconds, and makes it feel different, slower, less sharp.
The gun starts moving, hits the mercury, starts the mercury moving, the mercury steals impulse energy from the gun, when the gun starts slowing down, the mercury hits the back of it's container, transferring the energy back to the gun.
It's
not a miracle cure, it's one of those devices that obeys the law of decreasing returns. Little things that do a little bit, but can really start to add up $$ wise. Not useful for the occasional shooter, but all together can really help the dedicated, avid, gun nut.
The thing is though, is that there is very little mercury that you can fit in a guide rod, and a 1911 is already a heavy gun. If you can only stick an ounce of mercury in the rod, and the gun already weighs 38 ounces, then you really are only taking the top 3% at most off the top of the impulse curve.
That's not as small as it might seem, the top 2-3%

is always the worst 2-3%, but it is still just a percentage. If you are a casual target shooter you will just stop shooting when you get tired. It's only if you are a competitor that has to finish a match, and cannot stop because of fatigue, just have decreased performance, then it might be an important 2-3%.
**
In a shotgun or rifle stock, there's alot more room for mercury tubes. You can fit two 6 ounce tubes in the stock pretty easily, a much higher percentage of overall gun weight, and have a much more significant effect.