The Crimson Binome
Hero
The magnitude of the effect is too small, compared to the spell slot cost.What do you think is the main weakness. Bonus is too spell, duration is too short, simple fact of having to burn a spell slot period?
If you have a bonus of +1, then that will only change one-in-twenty failures into a success, and it's fairly unlikely that the party will fail twenty skill checks over the course of an hour. Even if they do, randomly converting one failure into a success is fairly insignificant, because it's random and you've already accounted for nineteen other failures going unmitigated. (That is to say, the skill check which was converted from failure to success was probably not a very important one.)
I feel like it would start to even out if you increased the bonus to +3. Even then, the spell slot cost would prevent them from using it on every single skill check.