Imo a big disadvantage definitely needs to be inherent to such a device, as i cannot see it working flawlessly even in the future. More fun if it was in early development and problematic 
I’d nerf it by giving it a chance to modify stats semi-permanently
Say, 5% to lower a random stat by one, 1% to lower a random attribute, plus a flat reduction to health for every “switch”.
The stats will return slowly (maybe with MTTH of weeks?)
EDIT - Yes i agree with the post below me so i did modify it a bit, plus gave some explanation on my rationale.