that could be verryy effective in crowded situations. how many do you think shoulg be in the game?
One.
But if you find a certain person who is an expert at alchemy then if you find the right ingredients then you can make him develop more.
But you're going to have to complete a series of quests for him, win a speech challenge, find incriminating evidence about him and blackmail him with it and only then can you make him create more of these for you.
(And not just one of these, you have to do all of these before he is willing to create any for you, one mistake and you have to reload)
You're going to have to work hard to earn the right for more of these grenades since they're instakill weapons.
The ingredients are going to be very rare and expensive as well.
All for the sake of balance.