I am borderline of what is considered a thick midget. Is it great? It is better than being taller and lacking any muscle thickness. I wear a large and it isn't too long in the body, or the arms, I have to say it is a standard sized large, the new wienie metrosexual sizing that has been coming out in certain brands recently really sucks.
What I like about loose rashguards is that I don't have something that feels like I am trying wrestle myself into and out of a small human sized condom. I usually only wear them while paddle boarding and kayaking back home during the summer.
Here is an interesting feature that I never used rashguards as.. Hawaii gets hot and humid, these shirts with the slightest breeze cool down. I have noticed the effect with certain climbing shirts and certain next to skin layers I have. I used my other loose rashguard more for staying comfortable while driving, walking around, or hiking to some remote beach somewhere.
While the shirt is not Loosey Goosey, it is snug through the chest and back, but it isn't like the body condom of the other Dakine rashguards I own, which I would never wear around town. We were driving to a beach first thing in the morning with the AC in on in the jeep I thought my nipples were going to freeze off, a little bit of perspiration and the slightest breeze is cooling with these shirts.
Plus, we have all seen the tourists who squeeze themselves into rashguards who look like a giant love handle spare tire, roley poley sack of goo. It isn't pleasant to see. This shirt would help with that to a certain extent.
For surfing? I think I would go back to the snug rashguards for actual surfing.
While it feels weird wearing a rashguard around, these make you feel less self conscious just milling about.
If you are fat? You are fat , nothing is going to change that fact at that moment, wearing a T shirt to cover it is like the fat kids in the pool wearing a shirt. "Oh look, a self conscious fat kid in a shirt.."
This shirt will help, but you kinda have to do your part the rest of the year.