I would suggest the following:
1. Make stealthboy work in the same fashion as motion sensor - it works for x seconds when activated and in active slot, then you need to recharge it with MFC or SEC. I would suggest 30 minutes, so you can synch it with drug timer.
2. Make it easier in general to detect sneaks, but instead make stealthboy increase sneak skill above the 300 cap.
For the last point, for instance, 60 bonus sneak from stealthboy corresponds right now to 10 hex visibilty. So you could increase the detection range by 10 hex, and make 300+stealthboy = 360 skill the maximum sneak skill. Then the best sneak is just as good as it is now, but to get there you need stealthboy. Without it, you lose 10 hex detection range.
I think the last suggestion would be good because then in order to have maximum efficiency, even if it's just to scout, you require some investment in terms of in game items. You can still sneak "for free" (without items), but you're then less effective. This would make it more of a reward to kill sneaks, especially if stealthboys are relatively rare.
If the item is not consumable the market will eventually be saturated, even if they only spawn in ares/glow lockers. So even though I think making it craftable could be nice, it shouldn't be strictly necessary in terms of balance - the item is common enough as it is. If you think you need more ways to obtain it, some other easy implementations would be: farmable from ROTMA, buyable through dialogue if you're member of BoS, additional reward for existing quest, spawn in some shops, lootable in random encounter lockers.