I would buy a pair of regular paddle fins (or whatever style suits you) and skip the freediving fins for travel. I pack all my dive gear (BCD, 3mm full wetsuit, booties, mask, regs, dry bag, lights, GoPro and accessories, and a pair of boardshorts; my computer is a watch-size so I just wear it) in a 46L carry-on size backpack. Fins (Avanti Quattros) get strapped to the outside of the bag. If I'm totally dirtbagging it I can get away with stuffing a couple of t-shirts in that bag too. Otherwise, I check a small bag for clothes and misc. stuff and toss my toothbrush in my carry-on with my dive gear. I've never had a gate agent give it a second look. In some aircraft I can keep my fins strapped to my bag and still fit the whole shebang in overhead. In smaller aircraft I take my fins off and put them next to my bag in overhead.
It's not always the most comfortable way to travel, since I have to haul a backpack through connections. But I'm kinda paranoid about airlines losing or temporary misplacing my luggage since it has happened to me so many times. I just got back from a trip to Bonaire where two of our group had their dive gear arrive a day late. It wasn't the end of the world for them since they just rented gear for the first day of diving, but it's still annoying. And they were both cold because the dive operator only had shorties for rent.
Not to hijack the thread, but don't freediving fins get in the way when swimming close to coral or through tight spaces? Asking because I have never used a pair and don't really know. Seems like they are specialized equipment for getting down and back quickly, not for finning along the bottom at an efficient pace.