The latest download is not compatible with Minecraft/Bukkit/Spigot version 1.9 yet and I'm not sure if I want to continue development of the plugin. ZathrusWriter made an unofficial update of the plugin that seems to work fine (although I haven't tested it). You can find the download for that here.
WorldEditSelectionVisualizer (WESV) is essentially the famous WorldEditCUI mod in the form of a bukkit plugin, which means that players don't need to install anything on their client.
Detailed documentation about the available permissions and configuration options is available on the documentation page.
This plugin has optional support for ProtocolLib (Jenkins build #74+). If you want to see particles from distances > 16, you need to have it installed and enabled in the configuration (see Documentation).

This plugin uses darkblade12's ParticleEffect library to spawn the particles. It also anonymously collects statistics via MCStats Plugin Metrics. You can read about the data that is being collected here. You can see the statistics here.