Unstable Injector can be useful for additional speed if your ship is taking Safety Overrides, because the SO range penalty is applied after the UI range penalty. So the range penalty from taking UI versus not taking it becomes very small.

Example, if you're using ~~Cryoblaster~~ Heavy Blaster, range of 600. If it's on a ship that gets SO, the range above 450 gets cut to 1/4 of the original value. So with SO, the new range is 450 + 150/4 = 487.5. If you now add UI, then the pre-SO range becomes 510, so the SO range becomes 450 + 60/4 = 465. So its range gets reduced from 487.5 to 465 if you take UI, or less than 5% range reduction, so then the additional speed may become more valuable.

This is only useful to certain ship builds and fleet setups where the extra speed is valuable, such as if other ships are using SO and you need the slower ship(s) to not fall too far behind. But UI can be useful in certain situations like this.