I have a gymstick and have been using it for the past month. I find it very good - it's quite hard and I definitely see a lot more muscle toning after using it more or less every day... and it really makes you sweat. I could barely walk the next day after starting out and doing all those squats and lunges. So don't overdo it, if you are not used to those exercises.
It may be a little pricey, I agree. But it is a proper tool and not some stupid gimmick, and it's also handy because it does not take up much room either. I know you can do the same with weights, but I always found them a bit awkward to work, and I therefore avoided them, which resulted in me getting too little anaerobic training. I very easily get bored and loose motiviation, so I have to ensure great variation in my exercise regimen and make sure it's fun, so I use the gymstick in combination with other training, like spinning, running, rope skipping, hoola hoops, (and even the dreaded weights once in a while).
My gymstick (medium strength) is blue and that is actually hard enough, since you have to do quite a few repetitions, and the resistance can be adjusted by rolling the elastic bands around the stick.