I have no experience of W 8.1 Before I finally settled on my security on my signature, I was trying Comodo, Online Armor and Zone Alarm firewalls in that order. They seemed to slow down boot up time considerably and of course the sandbox initialization. I did not try them without Sandboxie installed, so I can't say if those delays were normal. Compared to plain Windows firewall I was using before the slowing was really noticeable. And I would say also not acceptable from a user point of view. The first 2 lead also to BSOD somewhere on the while I was using the Firewall/hips thing. I can't say if those imcompatibilities would affect also the non sandbox involved times. I would think not sameas Bo thought too, but can't be for sure.