Bought myself this paint shaker after seeing a picture of one on Facebook. It’s a proper science lab one, meant for shaking up test tubes and the rubber cup is a perfect fit - if you use them - for those little plastic Vallejo and Scale75 bottles which are the hardest ones to stir. You can leave it turned on and it only activates when you press the bottle into the cup (you can also ‘bounce’ larger bottles on top of it to some good effect, it agitates the paint at the bottom which is hard to get moving.) It's a one handed operation, making it really easy to stir a paint bottle before using it - only a couple of seconds. Necessity? No, of course not, but a nice-to-have. This is the SciQuip Vortex Mixer (fixed speed) SP2260-FM, the most basic model. It cost £76 which might seem a lot but it’s also a lot more robust and useful than the flimsy paint shakers with straps being sold on Amazon and Ebay for £65 or more.