Pull ups don't really work well as you get bigger. Apparently the current L/XL size is about the limit of what actually works well. Adult pull ups really for people that dribble.
Convenience is a big factor. You can buy a small package from any grocery or drug store for not too much money and easily hide it in a backpack. If you started as a teenager this is a huge plus; and they probably fit you.
Agecomfort and rearz are the best for diapers. I used to get them from the local medical supply store before the jacked up the price of plastic backed abenas to the point it was worth it to order online. Rearz has some OK plastic pants and cloth diapers but their clothing it really pricey.
Even a small amount of hair on your butt makes cleaning up with wipes a exercise in futility. Even if you have someone else changing you it is probably best to use the shower to get properly clean or you might get wiped raw. I can't imagine cleaning poop out of fur would be possible without a...
Pull ups are a great thing if you want to keep well hydrated and not move. The pull up part is important because I have to be in a pretty good mood to enjoy a messy diaper. And if you don't make it that is an easier clean up than underwear.
I am sure if they raise $40,000 people will get their diapers. I think they set the goal at $40,000 because they don't think they will sell that many and it will be a weird promo.
Goodnites are the biggest of all the things you listed. Underjams are a bit smaller and when I tried them last the sides failed either when I put them on or soon after. Everything else you listed might stretch enough to get our legs through or close the tabs but will not be a very functional...
I kinda doubt they will sell enough for this to get funded an I think it was intentional. I have my doubts it is anything but a cool looking cover. It does not look thick.