I was hesitant to buy this unit for use with multiple Cat 6 Network Surge Protection Module's (PNETR6) after reading another review, but APC's website says that they are compatible, so I went ahead and bought one.
The two *do* work together with no problems. The PNETR6 fits perfectly in the PRM24, just make sure that the card is oriented correctly or it won't go in at all.
First off, there is nothing wrong with this unit. It does what it says--protect again power surge in Ethernet lines utilizing replaceable surge protection modules. But do not make the mistake I made and order this unit along with the APC Cat6 Surge Modules (PNETR6) that Amazon tries to sell you. The PNETR6's do NOT fit this unit. The PRM24 only supports the PNETR5 (Cat5 Module) as is clearly stated in the literature with the device. The circuit board on the Cat6 is too long and will only fit part way, so don't try to force it to fit either.