I just updated to STRIP 2.4.0 on my Mac (running 10.9), and I noticed one quirk about Secret Agent.
I run Safari in full-screen mode. When I tried to activate Secret Agent, it didn’t pop up. While checking why, I switched back to STRIP, to make sure it was running, and Secret Agent popped up for just a second, and then disappeared.
I switched Safari out to regular mode, and Secret Agent works right. It’s just when Safari is in full screen mode that it won’t work right. It looks like it’s trying to pop up in another screen, which of course doesn’t help me much.