Getting a Mara , scared of appearance/ will it be painful?

My orthodontist is suggesting me to get a MARA to correct my "class two over bite" , I have a few reasons why it is concerning me. First of all I have a very low pain tolerance , I was given spacers so they could take impressions for the appliance. These spacers still hurt horribly after a week, I've bearly been able to eat , even with pain killers. If the spacers hurt so tremendously I'm scared the MARA will be 10x worse , I've read online and even my own ortho said it was going to be painful. I'm also concerned that the device will give me awfully chubby cheeks (the receptionist told me it will give me puffy cheeks) , I know that should be the least of my worries but I have very low self confidence and I find my high cheek bones and jawline to be my best features. So that's another concern. I'm also not quite sure if it's highly nessacary to fix an over bite ? My mother , father , and brothers all have them and have been living a completely normal life without any TMJ symptoms? I just really want to know if I should go through this or not , I really need a professional opinon. Thank you (: