Rear derailleur on this set
Indeed as per the comments the 'lock' mechanism on Shimano rear derailleurs (to reduce chain slap) is called "Shadow Plus". Whilst this was initially a feature of the higher end models (XT / XTR) a few years ago, it has since filtered down to some lower models, such as SLX and Zee (although I think not yet on Deore ... anyone correct me?!)