Frankly I’m impressed that you tracked down what a marlin is, from a standing start in a world that you (probably) know little about. These pages are filled with topics that amount to “what is this bass, and is it any good?anyone ever had one?” Do well done
I was young when Marlins came out and quality has improved a lot with budget instruments. They really weren’t great and I’m not sure age will have improved them
I’d be looking at Harley Benton clones of the fender precision and jazz basses.
they cost pennies and are so good that many members on here gig with them (back when that was possible) or as a basis for small improvements
https://m.thomann.de/gb/harley_benton_electric_basses.html
they ship to UK for nothing (I think) and you can send it back if you don’t like it.
Get your son to join once he has found his feet. If he grows out of an HB you can shift it on here for a good price