Their traditional hair style don't look as good as Pururun's and Otama's... Also, Yattarou looks taller with his helmet on.
The main reason the males always keep their helmets on was lack of funding, heck the upgraded armors were only added at the request of the toy company selling the show toys. In fact said toys is why this show despite not having great rantings was able to last more that Eto Rangers and have a proper ending to the show. KNT did better on reruns but it is not considered a show iconic enough to have any characters cameo in Tatsunoko videogames, not even in that vs Capcom game.
Polly got to be able to get her helmet removed because she has a musical episode and that musical episode was made to help sell a music CD. Heck KNT had way too many music focused episodes to sell CDs and that is one of the reasons it is not as popular as it could have been.
However it was the earliest Anime to do the old Edo mixed with futuristic themes that I could find that wasn't a movie. Something both Saber Marrionete J and Edo Rocket did later. So the show did have some influence.
Also the show upgraded Armors do look a lot like SD Gundam.
Artwork itself isn't KNT/SPC, but still.
