I use cable ties and have done so for many years. It secures the zippers and keeps the suitcase from accidentally opening and may let you know if someone has opened them.
Locks on a soft-sided zippered suitcase basically give a false sense of comfort to the owner rather than actual security. Someone can open a locked (TSA or other lock) with a pen, screwdriver or knife as fast as you can unlock the lock. Once they have taken what they want they just run the attached locks and zippers around the case and it looks like it was never opened. I've done it a number of times with my own cases.
Go ahead and use the locks if it makes you feel better but locks keep honest people honest and that's about it. Cable ties do the same thing.