I’m setting up a Umerex Buckmark for my BIL eightieth birthday present. I’d like to put a red dot on it but I’ve never used one. I’ve looked online and see there are 2 basic types. One with a tube like a optical scope and open ones without a tube. Which is a better style for a low powered back yard plinker pistol? Any input will be helpful. I’m hoping to stay under $40 since it’s only a $45 pistol.