In Tasha's Cauldron of Everything p. 134, there is a magic item: Rhythm Maker's Drum (paywalled link). It gives a bonus to spell saving throw DCs (and spell attack rolls) of the user depending on rarity: +1 for uncommon, +2 for rare, or +3 for very rare.
Even though the same +X for a magic weapon is normal, and some weapons have specific extra effects, it seems a bit dodgy for spells, because that is +X for every spell attack roll, with all their different extra effects covered. But then +3 save DC for "save or suck" spell effects, like the 1st-level Ray of Sickness spell or the 4th-level Polymorph spell, just seems way out there at any character level.
Am I overreacting, is there something I am not seeing? Or is this drum, and any similar item, just something which a balance-concerned DM should not allow anywhere near their table, or maybe limit it to +1 version and making that very rare or something?
Reminder: I'm not asking for opinions. An answer like "it's fine" or "it's broken" must be backed up by facts (other items, rules quotes, official rulings, etc.).