I think these are pretty cool, I really like the colors, I think they could come in handy. It can help replace the majority of gel tabs for most people but you'll still need to use the gel tab in shallow substrate. I like the idea that it will continue to hold the opened fertilizer capsules, that way you can easily remove them and throw them away. These may have more uses rather than just for fertilizers, depending on the size of the basket you could put frozen food in them, like bloodworms or food for shrimp. I also think these would be really cool to grow moss on, you can put a little bit of moss on the inside and when it grows out you can trim it into a ball or whatever shape pleases you, and the spike will help you plant it into the substrate where you want it, and you can move it around whenever you like easily. I also think filled with moss you can take the spike and stick them into drift wood, or perhaps through a suction cup and put them on the glass. You could make some pretty cool designs for a moss wall that way, would be super easy to do a cross hatching.
The baskets also seem bigger than the gel tabs, so you can add more fertilizer so for well established tanks instead of sticking 20-30 tabs in you can put 10-15 baskets. The bigger size of the basket would also benefit larger plants and you will not have to refill them as often as you would have to replace the gel tabs.
The main draw back I see is the basket is solid, so it will always take up space under the substrate, so in order to have them under a carpet you would have to either grow plants over top of the basket and dog it up when you need to refill it or leave that area barren. Another draw back would be the fact that if buried too close to plants with fast growing roots their roots may grow into the basket itself, this may not be too big or a problem with certain plants but I personally try and disturb as little roots as possible.