Although this set of items has such a powerful effect when used together, it doesn't mean they're weak if used alone.
As a matter of fact, the Demonic Mask's passive effect allows him to strengthen all of his Spells by at least 20 to 25%.
From a certain perspective, it was definitely a lot better than the Energy Potion that Alchemist Sherah could produce in her laboratory.
After all, the Demonic Mask doesn't cause a significant strain on your body after usage. The only problem with the mask was the fact that he couldn't use it for long unless he repaired it.
That's right, both the mask and dagger were actually damaged. Vale had no idea how to fix it unless he brought it to an expert in the Academy. It may cause some problems if he was questioned about its origin, but that was the quickest way to do it.
He doesn't know anyone who could fix this outside the Vermont Academy anyway.