a self cleaning bucket... well mostly anyway... how many times have ya got a bucket full of snow and the snow stuck up inside of the corners? more so about mud / slop? granted with FEL you can racket the bucket back and forth and generally force everything out but a little bit here or there in the corners.
but when you have say a bucket full of sand, or loose potting soil, or wet concrete. and you have a flat shovel manually shoveling stuff from bucket to were you want it? no curves, just flat pieces to scrape edge of flat edge shovel against to get what you want as you want it. and no fussing with round curves. granted there maybe more risk of little bit more dirt sticking right into the corners inside the bucket... but... trade off of manual labor and clean out the bucket at end of day or those odd jobs. IMHO (in my humble opinion) well worth square / flat pieces of metal on the bucket.
i do a lot of "back dragging" with the FEL bucket. vs actually digging dirt with the FEL bucket. and for that reason. some sort of clamp on tooth bar, would be more preferred. (easy on / easy off) it is rare, when i actually need to use FEL to dig directly into hard compacted soil / rock. say digging into a hill side to get some fill dirt for some place else on farm = tooth bar, or trying to dig out a hump in a road / path in woods = tooth bar. but digging into already piled up loose dirt that backhoe made, sand that was delivered, drive way rock that was delivered, snow, tooth bar not needed. other words vary rare that tooth bar is really needed. and a simple straight edge has more advantage.
granted getting into live stock pens and cleaning up the slop and hay, and straw... is a different matter all together. and generally a pitch fork (long teeth) more likely wanted. vs general duty bucket with a tooth bar on it were the teeth are not that long.
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light bucket = mulch, it more likely wider and bigger overall volume it can handle. but it is also a lot weaker. and will not stand up to abuse like a general duty bucket would.