Again, tubular locks come in different strengths, much like traditional pin-tumbler locks. The latter are probably safer, but one advantage of tubular locks that makes them so suitable for chastity belts is that they can pack a lot into a very flat package.
Another advantage specifically for female belts might be that there is a company called Beaver Machine Corporation that manufactures such locks for use with their vending machines, and it might have humorous value to have a "beaver lock". Sadly, those locks are as self-picking as most common tubular locks, as the lockpicking lawyer amusingly demonstrates in this little video: https://www.youtube.com/watch?v=TRozAbaKs9M
