I've owned Kryptonite locks that have seized, I've cut my friends' Kryptonite locks when the tumble has broken. They're not worth $50. A cheaper U lock will do the same job. It's all just tempered stainless steel with a polymer jacket, no matter the manufacturer.
Paying more for a folding lock makes a little bit more sense because they have articulations, which can be weak spots if they're not over-engineered to compensate (Abus does this).
This is what you want.