| Without going into the game mechanics, there are some drawbacks to using the idea of a spell launcher or thrower. In my opinion one of the biggest drawbacks in the sense of an RPG is that there is the temptation to use them for the cool factor without bothering to describe how they work, what it looks like when they're used, cost and effort of maintenance, etc. In a game where details are important, using a gimmick like this can make things a little too easy.
It's possible to simplify the idea, no to be confused with making things easy, to fit within the setting. All you need to do is skip the bolts entirely. Using the pistol crossbow as an example, just say that when the bow is cocked it generates a bolt of fire or electricity. Recharge the crossbow with spells. Voila. There is practically nothing mechanical in this scenario which can violate the setting. Using the crossbow as the device also means you just follow the same rate of fire as the normal device, which satisfies a lot of questions about balance since crossbows aren't all that fast. Then you just have to describe what it looks like.
Just an idea of course. | 
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