What size of flat iron should I use?

I’m in a total dilemma. I picked out the brand new GHD hair straightener to buy but I don’t know what size I should use. From what I understand, hair straighteners usually are sold in one inch wide and one and a half inch wide sizes as their regular standard. But some people buy sizes that are bigger and smaller. I wonder if I should go with a small size ceramic flat iron since I have shorter length hair. Then I discovered the GHD mini styler hair straightener. It sounds like it would be perfect. The bars are only a half inch wide so it can work for both long and short hair. It sounds like something that would make styling much easier. I would like to go with it and try it out. But I also want to get a discount or coupon code to use to buy it first