when I first started playing, not a problem, but now that I am building up my supply of crystals and myth stones, my thumbs are becoming very unhappy. and my other fingers are telling me 'no way, the thumbs are saying it hurts too much!'
the other options besides scrolling the numbers by holding down the button, is a slider bar or typing in the number you want. typing the number might be the worst of the options, because of the keyboard popping up, but scrolling or a slider are the better options. the problem with the slider, is that the more items you have, the harder it is to get the exact number you want. with scrolling, you just have to get close to the number, and then tap forward or backwards to the correct number.