Holy smokes!!! 52oz would be HUGE!!!!!!!!!!! To be honest, I can't even imagine the resort making drinks in that kind of volume for all your guests. That would be the entire blender full of margherita I'm sure!
That being said, you're correct that there are smaller versions you could buy instead that might be a little more manageable and there are LOTS of brides that have bought them for their guests so I don't think you'd be out of place at all. And if you think about it, so many people would use them for day to day drinks here at home, so it might just seem that they are ugly in a beach setting??
We just bought a regular 16oz travel mug for our guests and figured they would be good enough even if we do have to keep filling them more often

We did personalize them but since I haven't actually received the order I can't even post a picture for you. As part of the imprint we had M*E*X*I*C*O in larger bold text and then our names and wedding date in smaller non-bold text. I really wanted to have something with our names and wedding date on it but we wanted people to (hopefully) use them again afterwards so hopefully we made the right compromise in text size etc...