Yes, as long as it is assembled as shown (rectangular), it is actually very stable. But not for older children to do gymnastics on...

Yes, absolutely, especially if you put the pieces that connect the barriers together. I've used it a lot without the suction cups. It's a great product and very reliable!
I even had one for outside and it worked perfectly!

Yes, it is stable. And a mat underneath helps.

Unless your baby is a professional body builder, yes.

An additional mat underneath is recommended for species-appropriate behaviour.

Yes, it has held up for us

We had also bought a children's play mat, which fitted in quite well. This held the palypen grid in place (the grid surrounded the play mat) and it didn't matter whether the suction cups held. Unfortunately, I can't tell you how it will behave without the appropriate play mat. In any case, we were happy with the combination purchase.