You may be surprised, The linear actuators I have seen using this technology are found in web guides used in the machinery that the company I work for builds. They move hundreds of pounds of mass easily with no slippage or loss of accuracy for years without adjustment. The feedback in that application is found on the servo motor not the actuator. As long as you don't exceed the load limit there appears to be no slippage.
That being said my concern would be in overloading the bearings and causing early failure. However the ABS plastic seems to have some flex that may reduce any overload. Time will tell and I am hoping that experimentation by myself and others will prove the superiority of this over belts and acme threaded screws.