This is an interesting question that has compelling arguments on both sides. But before we dive in, let's take a look at two different types of kendama.
An example of a JKA kendama
The kendama to the left of this text is an Ozora, a JKA (Japanese Kendama Association) approved kendama. This means that is approved for use in JKA kendama gradings and competitions.
All JKA approved kendamas must not be over a certain size, are only allowed to have glossy paint and there are restrictions on the sizes of the cups and the bevel. If the JKA approves it to be a kendama of good quality, it becomes a JKA approved kendama!
So, that's JKA kendamas in a nutshell; good quality kendamas that have certain restrictions. What's the problem? Well:
An example of a more modern kendama
This kendama to the left of the text is a Sweets Prime. It is an example of a more... let's say modern kendama. Even though I don't have one, I can tell right from this picture that the cups are much bigger.
The paint is tacky (this helps with tricks such as lighthouse and lunar, as it keeps the ken from falling off the tama), which definitely wouldn't be allowed under JKA regulations. Plus, the paint has tracking, which - again - wouldn't be allowed on JKA kendamas.
So, there we go. Two different types of kendama explored - the more restrictive but fair JKA model, and the modern innovative take on kendama. Where's the argument?
The question is - should tacky paint be allowed in competition - should it even be allowed at all?
On one side some people think that using more restrictive types of kendama is fairer - if everyone uses the these kendamas, the whole game is more of a test of skill. Some go as far as to say that tacky paint is cheating, and bigger cups make the game unfairly easier. Who cares if you can land a lunar on a Slaydawg - you have only truly mastered the trick when you land it on a TK16.
On the other side, people think that more modern kendamas are the way to go; with better kendamas, people can push the tricks that can be done to a whole new level. If it is a mainstream kendama that anyone can buy, why ban it? Another upside of more modern kendamas is that it makes kendamas more accessible to a wider audience - they will be less likely to get frustrated and give up on kendama. I honestly lean to this side of the argument, but it is super awesome if you can lace on an Ozora.
Tell me in the comments: WHICH SIDE ARE YOU ON and why?