When comparing a hybrid design surge protection device (SPD) to a single type component version there are a few general (and some specific) advantages. The statement “The whole is greater than the sum of the parts” comes into play for a properly engineered SPD. Case in point: the gas discharge tube (GDT)/ metal oxide varistor (MOV) hybrid circuit compares very favorably to the MOV only design.The GDT acts as a support to the MOV, allowing the SPD to successfully divert higher amplitude spikes, as well as larger power surges, with considerably less degradation than an MOV only type could handle. The MOV reacts first, diverting the initial spike safely to ground. The GDT diverts all energy beyond what the MOV max is. 
This is important since repetitive strikes are a common occurrence today. It also allows for longer warranty periods and greatly decreases the likelihood of equipment damage due to multiple spikes. Another advantage of this type of hybrid design is increased safety. High SCCR ratings and best in the industry nominal discharge ratings are a direct result of the GDT/MOV hybrid design.
The only supposed drawback to this specific hybrid design is that it will increase the VPR in UL1449 testing. There are two rebuttals to be had here. First – the testing is done with a very specific waveform that is considered “representative” but is by no means common in the real world. Bottom line is that the GDT/MOV hybrid design employed by PSP Products has been proven effective for years in real world scenarios. This is backed up by the almost nonexistent number of warranty returns and damage claims we have seen. This is supported by the ITI (CBEMA) Curve. This was originally used to verify performance on mainframe computers but has since been expanded to a wider range of business equipment. In short (no pun intended) most PCB operated equipment can withstand several hundred volts for a short period without obvious damage. Since SPDs operate in nanoseconds and spikes travel in microseconds, a device that has millisecond withstand is in pretty good shape.