Great for when you want/prefer the mouthpiece to be covered & protected from dirt, dust & debris. I use these for rails to trails (gravel) or when mtn biking when I know I'll be on muddy trails and/or trails that will be littered with horse poop. The plastic is thin & is easy to squeeze. Being made of thinner plastic they're easily scratched & scuffed up, but this is typical for all bottles.
This is a lightweight cage that appears to be very well made. I've only had them on my bike for a couple of rides, so I can't comment on how durable they are, but it looks good.
The cage holds my Camelbak insulated water bottles very tightly. These would be a good choice for a mountain bike or gravel bike where you need to worry about the bottles bouncing out. For a road bike, something that is easier to get the bottles in and out might be preferred.