The one I got has pockets etc that you can also put other items in as well as the more solid bottom. I dont like the perspex bottoms as I feel over time they could rub against the inside of the bag and create a little wear or hole, so I prefer to stick with the sewn (fabric or PVC type) purse organisers / shapers.
And the other thing that is great with them, is if you have several bags the same (I have 4 speedys) I just lift the inside out of one bag and transfer it straight in to the other bag - no need to rearrange.
I think with a NF you would be best to get one that is also a organiser so that things are in place rather than slipping in to the middle of the "big black hole"?