Few of my PTO shafts have that safety part. Most of my equipment is older than when those came out. You have to be 100% attentive all the time and you won't have an issue. If you or your operators are not that disciplined get it fixed correctly.
The lawyers have proven in court that it's the equipments fault people get hurt.
An example of this is the new saw I recently bought with a tag warning me that the "blade is sharp and can cause serious injury". With a little diagram of fingers being severed from a hand.