I tried the demo version (2.0.3). No slowdowns, no crashes at all. It is correct that it really modifies the System suitcase. I found the size of my System file increased about 48 bytes. I'll restore at the end of the trial period. But, I got no alerts from NetBarrier even I tested it with grc.com. Without NetBarrier I found my ports were Closed, and with the NetBarrier they reported as Stealth. I tried it with IPNetSentry with turning off the IPNetSentry's protection and made it to attack my system with its Test, but still got nd allerts from NetBarrier, I don't know why.