They really should be <1> or <2> to use them. One of the brand names folks use are aquatainers.
The biggest issue with things that are opaque like that, and have lots of nooks and crannies is cleanliness and sanitization, after the first use, you really need to make sure there is no biomatter, such as trub left in those odd spaces.
A good hot soak with oxyclean will knock most of the stuff loose, and then a couple thorough rinsings.
You may want to get a dental mirror and a bendy flashlight to do visual inspections afterword, to make sure there is no biomatter left in that.
They are fine to use, but honestly I prefer something I can visual inspect, like a standard bucket or a clear carboy.
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