Thank you for your question. No, those breakers are not UL listed for this load center.
You should only use GE breakers in GE panels as this is how product is tested with UL. Thanks for the question.
Thank you for your question. The P model is the newest version with a retail packaging label for better information on the shelf in stores. There is no difference between the actual product, just the outer packaging.
No. They use a screws to mount the top but the bottom slides into slots. You can turn the whole panel box upside fown though!
The home Depot photo sucks. The interior panel is rectangular, 14 1/4 x 24.68