Their JDM-explanation is pretty funny, but yes, these would have a positive effect on suspension geometry for lowered cars. How much of an effect just depends on how much the pivot center is moved in relation to the OE ball joint center. There are similar extended ball joints for the Mustangs; as I recall they moved the pivot maybe 0.5" lower. There's always a limit to how much you can lower that outer pivot; you're constrained by packaging/control arm clearance to the wheel, and also the longer that shaft on the ball joint is, the higher its operating stress.
So, basically it depends on how much you've lowered the car. If the new pivot is 0.75" lower and the car is lowered 0.75", then your geometry is roughly back to stock. If the car is lowered 2", then your geometry is still off by a lot.
But they're generally better than nothing.
And yes, bumpsteer is definitely something you need to take into account when making front-end geometry changes like this. When you relocate control arm pivots the bumpsteer will probably get very large. Hell even with a stock-geometry car, you could pick up some time on the track by tweaking the bumpsteer. OE cars usually have noticeable roll understeer behavior designed into them that you can mostly tune out with adjustable tie rods.