Keep in mind Aqua Blade is dual sword, not dual wield. That means you can equip two swords with aqua blade, but you can't do like aqua blade + a katana or something. It's still a nice TM, especially for Tidus (using Brotherhood + Aqua Blade for example). I farmed one myself but probably won't farm more than that.
Something else to consider is that we're now in the mog king rotation where we get TM's buyable in the mog shop. Last mog event was dualcast, which means the next mog event we get should have either dual wield or doublehand up for purchase for "free" (with mog currency). Knowing Gumi, they will probably stick doublehand in the next mog event and make us wait an extra month to buy a free dualwield materia, but it is coming, eventually. Those should be buyable on a 3 month rotation of dualcast/dualwield/doublehand.
If your best unit is Tidus, I would focus on gearing him as best you can. His enhancements should be "soon", probably within the next two weeks, and after enhancements, this would be an example build for him using mostly budget TM's:
After enhancements (which add an extra 70% passive atk) that would be 1090 atk. If you replace Bracer with Fury Ring (30% atk accessory buyable from fat chocobo after this week's maintenance) then his atk would go up to 1100 and you don't have to bother with the Bracer TM.
That's just an example of a cheap way to build Tidus. It can of course be greatly improved with rainbow TM's if you own them.