It's good. Even somewhat campaign independently good (meta spell-book knowledge good). There's very little in 5th that's actually broken or completely campaign changing that can't be handled by a competent DM though. So yeah. Good, and I consider it very good, but it doesn't "break" stuff other than meta-every-class-whole-spellbook-knowledge and Monster Manual stat knowledge. Which can sort of be fluffed away with double competencies and archetype "stuff" lore anyway.
edit: I guess it's like asking "Is giving someone a +4AC item broken?". Nope, not really. Although admittedly that doesn't ever use resources and is almost always in effect. Still, this can give any damage spell a +2DC and against the worst-save (about +2-3 DC effectively on highest->lowest save stats) rider on a spell. Damage or control spell actually. Or save-or-suck/save-or-die spells. Lots of resources used though. And auto-saves vs legendaries notwithstanding. But if it's an encounter deciding +5DC with the BBEG, is it broken? Not really. Or even the "cheaper" 2d10 force damage rider? Or the range one? No. But it's very good, with any spell, and can be very effective. But ~+4-5DC is huge with any element attached. Not as good as +4AC (resourceless, and making party threat a weirdly has/has-not thing), but it makes big spells bigger, and any of them. AC can be managed more easily by the DM due to what attacks/happens to the party member with the "higher than expected" levels of it. Ace-in-the-hole "whatever" spells with boosted DCs/any-damage-type could actually be trickier to manage, if only because it's a floating and variable ability.