I haven't used Franz, because it's not open-source. I actually found Rambox after hearing about Franz and searching for an open-source alternative.
Both Rambox and (as I understand it) Franz just load the web interfaces of the services you configure, so performance wouldn't be better than Chromium, since that's what Electron uses. The added value is in the wrapper, which helps to keep everything organized, lets you open and close all services at once (by opening/closing Rambox), and provides a global 'do not disturb' mode for notifications.