UniFi Stock Watcher tells you the moment something you want is back in stock on the Ubiquiti Store (store.ui.com). Pick the products from the live catalog; the app checks the whole store on a timer and alerts you with a notification you can click, a sound, and the product's page in your browser.
Each check reads the entire UniFi catalog, about 490 products in 8 requests, whether you watch one product or fifty, and a live feed shows everything that came into or went out of stock anywhere...