My main gripe with the Demolisher's 10-Dart Banana mag was that it only held 10 rounds whereas a 12-Dart straight clip (like from a Retaliator) took up less space with 2 more rounds in it. The straight clips are also easier to store in pouches for those bringing multiple mags to the fight, like my buddy at Basic Nerf, so I couldn't really see a benefit to this kind of mag in the first place. I can only guess that the 15-Dart Banana mag will be about the size of an 18-Dart straight magazine and... even if it's not... it's still got a shape that's more difficult to work with.
As a result of these two new magazines for Clip-System blasters, I've got to start wondering why the need to make things look "Tacti-cool" has started to negatively effect their usefulness? Nerf has done a great job including Tactical Accessory Rails, nifty sights, and awesome-looking designs that accomplish the goal of making these new blasters quite pleasing to look at... but none of them have ever really sacrificed usability. These banana mags, in my opinion, are crossing into the "tacticoolness over usefulness" realm.
There's still a place for these magazines when you're not looking for a tactical advantage in a game. It's really just for show, like a lot of the other accessories and bits that you can put on Nerf blasters. Dress up your favorite blaster with a Banana Clip and BAM! You look pretty awesome! Try and load up your rig with 6 of these in pouches... and you're not only going to run into problems with storage, but you'll find that if you had showed up to the fight with 12 or 18 dart magazines, you'd be able to dish out more shots, too.
At the end of the day, from Tactical Tag's look at things, these are about as useful as those coveted Nerf Pinpoint Sights. They look cool, they have some functionality to them, but when it comes down to it, you're better off with something else. I'll take my straight mags unless I'm going for pure style and looks... and who goes into foam-dart combat like that?