Bag did exactly what I needed. I had questions before I bought it and none of them were answered to my needs. So I thought well, I'll just try it out and hopefully help someone else in my same predicament.
The other day I flew with Allegiant Air. Their pet bag requirements say the bag needed to be 9" in height. This bag is 11". I was worried it wasn't gonna fit under the seat, Allegiant wasn't gonna let me use the bag for my flight, it's not bendable enough to fit in a 9" area if I absolutely needed it to, etc. Well, after being set up and ready to transport, the bag isn't really bendable. From a durability standpoint that's good. But what I needed, not so much. Again, the bag is 11" and I needed it to be 9". The description lists Allegiant Air as one of the compatible airlines that this bag works with despite it being too tall in height, which was one of the deciding factors I ended up buying this bag.
Anyway, I get to the airport, they don't check the bag's dimensions. I get on the plane, and slide the bag under the seat. There's still about an inch of space in excess above the bag. I'm definitely relieved. So if you're flying Allegiant and are looking for a bag that's big but still works, this one is for you!
The top opening is great my dog loved poking her head through it. All the side openings are good. I didn't use them on the plane though. My dog had enough room without opening them. She's a 16.5 lb. Maltichon.
All in all worth the price and worked with Allegiant. I would buy it again if I had another dog, and will be using my bag for many times to come on all my future trips.