Accurate Staff of Defense +2

This staff can be wielded as a magic quarterstaff that grants a +2 bonus to attack and damage rolls made with it. While holding it, you gain a +2 bonus to armor class and spell attack rolls.  

Above description taken from other 5e game magic staves standard.  

Accurate Staff of Defense has 10 charges. One charge as Reaction (formerly immediate interrupt) to apply spell casting ability modifier to defense (i.e. same effect as 2nd level Shield spell to AC but scaled lower unless caster stat is 20).  Can be used after damage total. 1d6+4 charges regained daily.  

Details:  Made of primarily of fine grained oak inscribed with symbols surrounded by intricate pattern, it is a +2 attuned spell focus and weapon alike the other 5e mid-bonus arcane staves; but it is limited in that it only has the use of the Shield like single effect for its charges.  

Unlike the glass material of the better known 5e Staff of Defense with which it is similar, this staff has a look, focus and martial weapon bonus more similar to other 5e arcane implements. It is more quarterstaff weapon like than, but also closer in appearance to other arcane staff.  Otherwise it functions similarly to the more common Staff of Defense in the 5e game.  

Like the Staff of Defense, charges are used for the 2nd level spell equivalent effect.  The effect of which instead of a Shield spell with a full +5 bonus, it is adding the spell attack modifier of the staff user, which requires a 20 in spell caster stat to have an equivalent +5 effect.  Like the spell, it channels power (force) from a planar source for its effect, but it is not directly the same as the spell as it draws attuned user scaled power at a more raw level.  It is not a spell in this way, but in 5e the shielding effect is the same.  It is directly channeling power, not a spell.  The shield effect is the same otherwise, boosting AC with channeled power.  See 2nd level spell description.

TL;DR Recap 1:  The 2nd level spell equivalent Shield effect is a scaling weaker power of the spell caster's stat bonus until the caster stat is 20 at which point it equals the full strength of the second level spell.  The effect is the same, but it is raw channeled power, not a spell.  

Unlike the Staff of Defense, it does not have mage armor casting capability.  Its spell effect is a measure of the users base stat ability to conduct channeled raw power for the equivalent Shield like effect only, but requires the caster's stat, INT, WIS or CHA to be 20 to equal the power of the 2nd level spell.    Like the more common 5e game Staff of Defense and other 5e game arcane staffs,  the Accurate Staff of Defense boosts AC.  

TL;DR 2:  The Accurate Staff of Defense is accurate when making spell attacks with a +2 to spell attack and it can be used as a Quarterstaff +2 alike to other 5e game magic staves.  Like the Staff of Defense and other 5e staff, while holding the staff, there is a bonus to AC.  

Rare 3.5e, 4e, back to basic Roots D&D, Fate, 5e translated legacy attuned staff wizard implement focus +2 magic accurate staff of defense weapon. 

Notes: Bonus: Spell Attacks, Bonus: Armor Class, Weapon Property: Versatile, Damage: Bludgeoning, Bonus: Magic, Buff, Combat, Focus