A major benefit is that heeled bullets are not very aerodynamic and can only have the one heel configuration which requires manufacturing in a unique manner. The .21 approach is the same as used in all other rounds, allowing different heel configurations as used in more sophisticated, standardized manufacturing procedures. In a nutshell, it provides a rimfire round with the capability to emulate modern centerfire manufacturing requiring only a slight modification to the gun's chamber. The question is, will these advantages provide enough marketing and sales success to justify guns having the revised chamber even with the expected improvement in bullet selection. It's not expected that the .21 will replace the existing classic .22LR ammo and guns. We shall see.
Whether the non-lead bullet will be a winner in and of itself remains to be seen. The .21 could still use lead bullets where it seems practical.
I think te article does a pretty good job of covering all the features and considerations. JMHO