There is basically no resistance. It's difficult to guess a resistance without holding the device in hand, when buying one online. But this is basically for someone that has completely disabled fingers and is trying to move them for the first time. For training fingers this is too easy. Look for a stronger resistance. Otherwise the product is ok.

It does exactly what it says. In a second-hand case, it helped a lot in finger and overall hand training. I was afraid it might be too soft, but the medium was actually a little harder than I expected, which of course was the right thing

I bought it for my trigger finger condition. It can exercise each finger separately, even the thumb. A relatively strong hand could start from the immediately next hardness level (the blue one), as the medium one seems easy to me and requires many repetitions if someone wants it for strengthening the grip, for example.
Sturdy construction that seems like it will last a long time. I specifically lubricated it with silicone oil on the springs.