This is a must have if you have the SS Brew Bucket. This makes it easier to manage possible overflow during early primary fermentation and it can also be used for closed pressure transfers into your kegs after fermentation is over. For $20 this is an easy and inexpensive upgrade..
Works great, used 1/2” silicone blowoff for initial “heavy” yeast activity then switched an airlock attachment I made by threading a piece of the 1/2” silicone through a PVC elbow to add rigidity. A #4 silicone stopper fit inside to fit the airlock onto. Works great.
I dislike stoppers and bubbler type air locks for several reasons. This thing makes the brew bucket more compact and IMHO more stable with a range of fermentation. I haven't tried it yet myself, but I've seen folks on YouTube use this fitting to close transfer beer into a keg with co2 from the brew bucket.