1-They are lighter, thinner, more flexible and don't chip.
2-You get 15 in a set for about $25 compared to 5-7 in a comparably priced Spellbinder set.
3-Because they thinner and lighter they stay put on a magnetic storage page.
4-Because there are so many, they nest in a way that allows you to make perfectly spaced frames by cutting several at the same time.
5-They sizing is so much closer that when you use one for a mat layer it barely peeks out from the main layer. No trimming it down.