I've used a Zumo for , well ages, since they first appeared, and I've never had a problem with the screw or loosing the driver. 
        
 
         
         
         
         
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               Originally Posted by 
              driesie  
              it takes seconds to remove the cradle from the ram mount
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         Cut off the 'lugs from the RAM Mount, I did on one of mine, made it into a 15mm 'nut' with only two flat sides. 2 advantages, one being you can tighten it up far more effectivly, 2nd being it becomes much more secure.
         
        
 You might want to conside making a new driver, rather than make a thumbscrew ? after all it's only a standard flat blade scredriver with a small slot missing ??
         
        
 With the security screw in , it does become more secure against theft, it's still only anti-snatch, but they are the thefts you can protect against rather than the determined thief who set's out to get it.
         
        
 Since moving to the Tenere I have fabricated my own mounting bracket and added this to a Touratech ant-vibration mount, this has an additional locking flap that adds a little more security (agianst vibration, bumps etc) for the unit.