Bandos tassets are a part of the bandos armour set, requiring 65 Defence to wear. They are dropped by General Graardor and his bodyguards in the God Wars Dungeon. Bandos tassets are widely used by experienced players as they offer superior stats compared to similar leg slot items, including the highest strength bonus.
Bandos armour is arguably the most powerful non-degradable melee armour in Old School RuneScape, and bandos tassets have the highest offensive stats of any melee legs slot item. For this reason, it is a common selection for melee training, Slayer tasks, and other prolonged combat encounters. Its excellent ranged protection along with its strength and prayer bonus makes it popular for some boss hunting scenarios. Stat-wise, it is comparable to barrows platelegs, which provide almost identical ranged protection and significantly higher melee protection. However, most barrows armour does not provide any strength or prayer bonus and degrades.
The most comparable piece of barrows armour is verac's plateskirt; its +4 prayer bonus, higher melee defensive bonuses and lack of negative magic defence bonus makes it a very feasible substitute given its lower cost.
In comparison to other non-degradable options, obsidian platelegs have 1 less strength bonus and 25 less stab defence, 20 less slash defence, 25 less crush defence, and 53 less ranged defence, but are significantly cheaper. Dragon platelegs are also much cheaper and offer similar melee protection with 3 less stab defence, 3 more slash defence, 3 less crush defence, and 28 less ranged defence and no strength bonus.
For an exhaustive list of all known sources for this item, see here