Quality depends on what you use it for.,
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This review is from: GMYLE(TM) Handheld USB Trackball Optical Mouse Mice Laptop PC
I have dystonia, a normal mouse causes me great amounts of pain. So I bought this as an alternative.
Build quality is variable the unit itself is good, but the ball feels a little flimsy.
For use though it depends on your purpose.
For surfing the net it is great 5/5
For working 4/5. It is comfortable for long periods, but hard to be precise, such as editing a document.
Gaming 3/5. Fine for anything turn based, in fact it is ideal for Civ or anything like that, but anything that requires quick and precise action will not be practical such as an RTS or action game.For those I prefer a Kensington normal trackball.
In summary. It is great for surfing, reading and casual work, but will not suit anything requiring quick precision. If you have a medical condition that requires a mouse alternative this will do the job, it is comfortable and inexpensive, but I keep a regular trackball plugged in for the important stuff.