They are great cranks but they can develop hairline cracks and then break completely. There is a common fix if they have not already started to crack. At the arm on both sides where it transitions to the spider the edge is very sharp and acts as a stress riser. You can use a narrow round file and round out that area and it will prevent cracking. I have even seen cranks that do have fine hairline cracks there saved by filing past them and making the profile rounder.

The Mavic cranks are nice but are in fact a copy of the Campagnolo cranks and were not made by Mavic but for them (by Gipiemme if I remember correctly).