I think the brigittae will be fine. I have them in a 15 gal that my girlfriend is currently taking care of for me since I couldn't move it with me. They look nice, and the Mr. Aqua tank isn't that much bigger. You can certainly add them no problem. And they are a very nice and active fish species, so I think they will be just fine. Another, additional benefit, is that they have a smaller bioload, unless of course you dump 50 of them in there, so the parameters should be nice.
Are you hoping to see the inhabitants more under close observation or from far away?