Tiples were mostly used for Central and South American music, Mariachi and other styles of that type. These days, a lot of people tune them like ukuleles (as you mention, GCEA) and play them as ukuleles with more strings.
The Regal brand was used by a Chicago, Illinois company throughout the first half of the 20th century making stringed instruments including ukuleles, tiples, guitars, and resonator guitars. They also made components for National and Dobro. Their instruments aren't thought of with the same regard as Gibson and Martin of the same period. But if you picked this up for $100 and it plays in tune, you got a pretty good deal.