There are two kinds of buckets, mineral supplements and feed buckets (you can tell the difference by looking at the protein content in them, for mineral supplements it'll be <3% but for feed buckets it'll be 12-18%). For tupping (and/or pre-lambing) you want a feed bucket.
The other main brand is Crystalyx, they do a red tub called Extra High Energy.
Some sheep are greedy as Hillview Farm points out, but if you find they are eating it too fast then check that they have enough forage and try putting the lid on it overnight to restrict their intake. Crystalyx claim you should be aiming for 150g per ewe per day for say tupping, and 200g pre-lambing. But of course that will depend on your forage and the weather etc.
Some tubs also contain Urea which is supposed to encourage the sheep to eat off all the lesser quality grass I think (but I stand to be corrected
).