There are many iTunes M4V converters in the market that has the ability to convert iTunes M4V to MP4, the difference may reply on the quality, speed, design...
NoteBurner is good, check the
review for NoteBuner M4V Converter Plus.
Tunekit is a new comer, check the
review for Tuneskit iTunes DRM video converter.
If you wanna know which is better comparing Noteburner and Tuneskit, then you should not miss this article
iTunes M4V Converter: Noteburner vs Tuneskit.