I love the stress free cutting with this cutter, and have found Martelli to be very willing to replace parts. They have replaced the bolt for me, and advised that I was pressing too hard.
Their videos are essential in understanding the proper way to hold and clean the cutter. You can easily pop the spring off when cleaning if you move the guard too far. By the way, I recently bought the Martelli cutting mat and have found that the blades last much longer when used on their mat.