But is the finish from a plastic float actually bad enough to vent about? Most times those little marks fade or get worked out with later passes. It sounds like a minor detail that gets blown out of proportion.
Well, it drags the compound differently than a metal trowel and sets those ridges deeper. You can spend twice as long sanding them out later if you don't catch it. For a small patch it's fine, but on a big wall it becomes a real time sink.