Today there are many who seek perfectly balanced Sai to practice with. While this is OK I believe there is a case to use unbalanced weight Sai for your training.
It is rare that you would study Sai today for instant self defense needs. While they might exist it is doubtful that those circumstances should dictate why you select Sai for practice.
In my opinion, the purpose of Sai study is for deeper purposes. The reason is for deeper purposes than retaining a part of Okinawan culture. The study of Sai becomes a long term force enhancer to your training.
I see what the Sai training offers over the decades of training. Your work strengthens your arms to make your open hand techniques more powerful. I realize it is difficult to understand this use. However, having trained myself and some of my students for such a time, I have come to understand this purpose.
Long term practice involves strengthens the grip, fingers and builds arm strength. Each of which contributes to the Karate application use in application. As we age it allows us to improve when life wants to tear us down.
Now the additional logic for imperfect or unbalanced Sai. The true balance for your sai comes from decades of work. You will learn internally, through practice, how to make the imperfect perfect for you.
Should others attempt to use your Sai they would be imperfect for them, without the years of skill building you spent. Theoretically should they attempt to use them against you, the Sai would not be readily familiar in their hands.
But though perhaps plausible, the additional effort over time to make their use perfect for you outweighs this consideration, to my way of thinking.