The bigger size would be best for two cockatiels, but the smaller size would work if they're good friends and get a lot of out of cage time.
"Cheap and flimsy" is a good description of it, but it's a useful, practical cage all the same. It can be folded up to lie flat when you're not using it, and I have some extras that I keep in the garage and set up when I need them.
The door slides upward, and then you can tilt it so it stays in the open position. When it's in this position I use a safety pin to secure the bottom of the door to the main cage so it can't be accidentally knocked out of position and come crashing down. If you look carefully you might be able to see it in the pictures that are coming up.
I also put a rope perch on the outside of the cage that the birds can use as a "porch" when they're coming in and out of the cage. You can also make a perch from a curved branch to do the same thing.
The door is big enough that I can easily bring Dweezil through it on my hand. I didn't use any actual birds in this picture because I figured they wouldn't be too happy about the camera, but you can see how big the door is compared to my fist.