Custom Google Search multisite vs. single site searches

I'm configuring my production (multi)site now, and am looking for a good search plugin replacement to the default WP search. I'm intrigued by the WPMU Custom Google Search given its ability to search across sites in my multisite, but I would need searches to sometimes be restricted to the site in which they are entered. How does this work with this plugin? For instance, if network activated does the plugin automatically search all sites in the multisite, vs. if activated by individual sites does it search only within that site? This would imply that one could not use this plugin to accomplish both.

Many thanks,

Jim P.