The Intilab one works perfectly, only minor downside is that you have to hold the paint bottle in the shaker whereas with the nail polish shaker you just stepped it in and let it shake.
With larger paint bottles such as Foundry or GW, you have to find the right angle and pressure to apply to get the mixer to vibrate.
So, a couple of irritations but it has been used a lot over the last 3 months and never let me down.
It will not improve your painting but it does improve your paint by mixing it well and that helps to give a better finish.