The Model 32 not only removed the folding wingtips but also carried re-located and re-designed flaps and ailerons. This also eliminated the need for the underwing mass balances. An enlarged underwing bulge was added to each wing to collect spent 20mm cannon shell casings from the increased number of rounds added to each gun. After all of these time consuming changes, the Model 32 performed no better than the Model 21 due to the smaller wing surface and added weight. It's major shortcoming was that it suffered decreased range vs. the Model 21. One does not want to decrease the range of one's fighters during a naval campaign fought from carriers and island bases while the enemy is increasing the range of his fighters. Thus the return of the earlier wing.
Be careful of the 21st Century kit. The original Model 21 kits had the Model 22 cowling by mistake. The air intake for the Model 21 is located at the bottom of the cowling whereas the Model 22 had the air intake on the top of the cowling. The engine exhaust was relocated on the Model 22. Also, the Model 21 cowling had open gun troughs whereas the Model 22 cowling had enclosed gun troughs. Later issued 21st Century Model 21 kits had the correct cowling. This mix-up has created much confusion among modelers.
One cool thing is that the Tomy/Swallow/Doyushu kit has the downturned wingtips that were added by to lower the stall speed of the aircraft. This was one of those simple but brilliant solutions that the Zero's chief designer, Dr. Jiro Horikoshi, came up with because the early Zero's were experiencing stalls at the design landing speeds ("Eagles of Mitsubishi - The Story of the Zero Fighter" by Jiro Horikoshi). One might suggest that the Tomy wingtips were simply warped but I favor the more exotic explanation above - that's my story and I'm sticking to it!