Plugin Slows down site admin

I just installed and activated the 2.1.5 version of this plugin and I think it has great potential, for client sites, because it does work and it does what it claims, however it seems to slow down the admin section of WP a lot! I only have this installed on a local system, so I can’t grant the author access to test, but after de-activation, everything in admin went back to super-fast. I have created a simple plugin to replace the login logo, and that works okay for me for now, but speed in admin is very important, especially for impatient clients. I’ll give the author the benefit of the doubt and not submit a bad review because the plugin is not bad.

http://ww.wp.xz.cn/plugins/custom-login/