Those things are typically made from Homopolymer Polypropylene, which isn't a particularly durable polymer, especially when moulded in a thin wall application such as those tubs. Long term, or even short term, I would not trust them with water in, and sure as hell wouldn't trust those cheap castors which are bearing the weight.
What those things are good for, and what they're designed for, is for space saver storage of lightweight articles, such as seen in the picture. If you are going to use such a product I suggest you store hobby related stuff in them such as old pumps, filters, heaters, media etc etc etc, and NOT fish!