Just get one.
It's nice to have some type of cover over the nozzle on any water bottle. It keeps the road grime off of what you're putting in your mouth. It actually helps your grip as you can leave the top on when you open the nozzle by pulling it up from a cage, flip the top off with one hand and drink. The ring on the other end fits nicely into a groove on the nozzle. It's a no-brainer for a Bivo bottle if you're a person who wants to keep the drinking nozzle clean while riding.
It's not something I thought I needed, but once I tried it, I loved it. Keeps the dust and other dirt out of the spout making for a cleaner drinking experience. Easy to take on and off without having to look down. Bivo should just add it to the bottle and not make us pay separately for it - come on, Bivo.
