Can u explain why. I thought one is a firewall and the other is strictly a white list.
SpyShelter Firewall is not just a firewall. It has application white-listing as well. There is some duplication of function between SecureAPlus and SpyShelter Firewall. Consequently, it might require double configuration and\or you might have to respond to double alerts.
Anyhow, I looked at the SpyShelter site. They changed Restricted Applications to Sandbox...
so, with this change, it might work OK with SecureAPlus.
Just something to think about if you start to get double alerts. In my experience you are attempting to combine too many security softs... but that is just based upon my own personal experience.
It just might work well for you on your system and for you personally...