another pro nine chest protector question

[Dakota]

I don't have a pro 9, or the seemingly similar Honigs K-1, so I have a couple of questions (since I'm considering getting something with better protection than the Honigs K-2 that I use now).

1) Are the Pro 9 and K-1 essentially the same under different names?

2) What is the function of the problematical side flap? (It seems from the picture to be of marginal use.)

3) Does anyone use the K-1, and do you have the same issue with the side flap poking out all the time?

I really don't want to have to wear two shirts under my umpire shirt, so if that is really required with the Pro 9, that one is out for me.