I used to grab whatever cheap trowel was on the shelf. After a bad bend ruined a long inside corner, I switched to Marshalltown. Their corner tools are thicker steel and just don't flex the same way.
My buddy had the same thing happen on a big fireplace job. He was using a flimsy store brand trowel and it just folded over on him mid-pull. Left a huge wave in the mud that took forever to fix. He swore off cheap tools that same day. Now he won't touch anything but a Marshalltown for corners either. That flex is a total job killer.
Oh come on, one bent corner trowel and now we're acting like it's some kind of tragedy? I've used cheap ones for years and yeah they flex a little but you just adjust your pressure and keep moving. Fixing a "wave in the mud" from a bent trowel sounds more like a technique problem than a tool problem to me.