I agree, regular luggage works for me too! I stuff everything besides my wetsuit and spear into a samsonite carryon (bp/w, regs, lights, reels, smb, etc.) and strap my fins to the outside of it since they're too big. I guess I'm advertising what's inside from the fins, but that bag NEVER leaves my side... until it's time for those damned shuttle rides, then I watch it like a hawk! On the way home though, sometimes I'll just throw it all into a larger suitcase and check it.
I guess the nice thing about the "dive caddy" bag is that it folds open and I guess you're able to just open it up and send it through the x-ray machine at security... but given my personal appearance, I'd probably have to separate it all anyway (no joke, I've once been interrogated while the bomb squad went through my stuff... I've since learned it's just easier to separate everything. On my last trip, I sent 9 trays through the machine! You don't want to be behind me in the security line! haha).
Also, possibly scuba specific bags are less 'plush' on the inside (never had one, so I don't know). But the nice interior of my bag got beat up pretty quick.