Thanks very much for writing this plugin. It does what it says on the tin! I have been able to secure pages very effectively with it on my sites.
The only issue I have is that on one of my sites where I am using a non-standard WordPress theme and customised home page, I don't get the message displayed -'You don't have access etc..' come up when I am redirected onto the home page. But I guess this is probably the code in my homepage/theme that's preventign this.
Sure, happy to donate something :) You should start accepting BitCoin donations though )