The interface, support for multiple languages (including Russian), ability to send emails from any device with internet access - no need in an office or at home desktop computer. You can use it as long you have Internet connection available anywhere! I didn't like how often there was some time lag between writing tests/emails during execution phase when using local development environment compared to my remote workstation where everything works very fast. If someone needs simple yet reliable tool which helps him check if his code will deliver expected results before going live then this could be perfect fit. We're solving problems related to our web applications by checking user-friendlyness via automated communication through mailable messages sent out after each change we make into source codes.