I've got a Simplicity Sidewinder. It's the smaller one of the two available and runs on batteries.
I got it at a time when winding bobbins was a problem for pretty much all of my vintage machines, for one reason or another, and I was down to winding all bobbins on my 1990s Bernina. I was afraid that if that machine let me down, I'd be stuck with no reliable, faff-free way to fill a bobbin.
It's OK. I've never had any major problems with it, and it does the job, though it always operates at a rather sickly speed and has a flimsy feel to it. There is an option to power it from the mains (cable not included), rather than batteries, and I do wonder if that would perk it up a bit.
I've used it to wind class 15 and Singer class 66/Elna bobbins. Always from small/medium sized reels so I can't comment on how it would behave with large cones, but I can't imagine that it would work well. I still use it from time to time if a bobbin runs out when I've got something with a lot of pins held in place under the presser foot and I *really* don't want to unthread the needle.
I got it fairly cheaply on eBay (<£20) and for what I paid for it, I'm glad I have it, but had I paid much more I'd be disappointed.