Many of the Tuners have useful effects, such as Synkron Resonator which will add another Resonator from the graveyard back to the hand when it's sent from the field to the graveyard (which is easy to do with Synchro summoning)
To determine the exact value, you should consider the card's condition, rarity, and demand
Even if you don't have the creatures to charge it, its enter trigger lets you search for a legendary creature and put it into your hand
By discarding a Level Five or higher Danger
Although the obvious advice would be to buy whatever is available to you, given the set's high demand, certain products are better options than others
emergency : The attack power of one monster selected as an attack target is increased by 600 until the end of the battle phase