I pressed the order button for a U.K. supplied one a week or so ago (unnamed / 'white box' type) and have used it on four bottles of paint with mixed results:
Army Painter white - currently like sludge but slight improvement
Army Painter red - normally clear liquid comes out first but now good coverage
Vallejo blue (no idea the actual number) - similar to the red but now great coverage
Flesh (AP I think) - better but it's taken a good three to four minutes to see any improvement
All bottles have agitator balls in them (a mix of rusty eBay and decent Army Painter ones). Oddly the rust does not seem to bother the paint after a year or so (not proud on that saving) and two balls do not seem any better than one.
My paints are anything from six months to four years old and so far it's a reasonable win for me. Not the panacea YouTube shows but it will cover its cost over buying / trying paints.
Biggest drawback was the cheap 'euro' adapter and two pin mains block. Risked it once while I was next to it (and excited to try it) then dug up a decent 12V 3Amp adapter from my 'spares'. I see
the eBay link now states EU adapter :-)