DRM removal software 5star freeTunes and MuvAudio can convert from .m4v to audio files only.

I know only one DRM remover that can convert .m4v video files. It is Tunebite Platinum, already mentioned by you. You can try it before buying it to make sure it works with your .m4v files.

In many cases DRM removal tools have problems with the latest versions of players like iTunes or Windows Media Player.

If you install an older version of a player, you may try to re-download video files with it. Make sure they won't charge you for that.

You may re-record your video files using screen video capture software like free CamStudio.

DRM removal tools like Soundtaxi have an advantage of saving ID3 tags and filenames when re-recording audio files. Besides some of them can record faster then in Real time. Moreover you can use your sound card while recording.
But you can save some cash if you download complete albums and use tagging and renaming software (of course the DRM removal process will take more time for you in this case).

As for DRM removal software for video files, its advantages are rather controversial. In many cases screen video capture software will suit you fine. But you can always use free or free to try software to compare what program will be better for you.