Never used the ZPI and I have not used the KTF enough to give an educated opinion. There are different Avail Spools for the Aldebaran MG7/MG, XT1000, Curado 50E, Core 50MG7 and Chronarch 50E reels. Japan Tackle has a description of how light each spool is capable of casting. I have the most experience with the Yumeya 32mm spool. It is a fine spool that is plenty capable (with the right rod). If you go to YouTube and watch the Shimano BFS Videos where they are using the Poison Glorious, Poison Ultima BFS rods etc, you will see that they are not using 1 gram jig heads with 1 gram plastics. Americans have a different definition of what BFS is as opposed to the Japanese that invented it. They are tossing 6" worms and hard baits that don't look BFS to me. My Shimano BFS rods are rated from 1/8 to 3/8 of an ounce and my Megabass BFS rod is rated from 1/8 to 1/2oz. 1/2oz is not very BFS is it? Well, that is what the rod is rated for and I think it even says BFS on it. I have evolved in my BFS fishing to when the conversation gets into casting a lure that weighs the lightest possible weight, I don't participate because that is not what I do. With my BFS combos, I am tossing Keitech 5/32 oz finesse jigs with a trailer that probably weigh a 1/4oz true weight and I use an 1/8 tungsten bullet weight with my light t rigs. I can easily cast 1/16 oz bullet weight with plastic but I am not happy with the distance. I am also using 1/16oz jig heads with the little 2.8 and 3" Keitech Swimbaits, Super Fluke Jr's and my Flick Shake Jig Heads are 1/16oz.
Do you how light in total reel weight or how light it will cast?
Other people can comment on the bearings.
The Avail spools are great. I have the CNQ5026R's in my Conquest 50's and one is mounted on an MSX-X Limited BFS rod. It casts a Super Fluke Jr. considerably farther than my KTF Spool equipped Aldebaran Mg7/Poison Ultima. I do have different lines on each reel but the difference in distance is very noticeable.