They don't seem OP in my limited experience. I'm in a Cobra doing assassination missions. if I'm not careful and an anaconda takes me to 0 shields, I can't even use the thing until my shields reactivate, which then means 4 pips to sys to speed it up ... etc. Also, the shield cell only recharges over time, it's not instant. In one fight I was at one shield bar, I used a cell, while under fire, and I was taking enough damage that the shield never got beyond 1 bar before the charge ran out. Perhaps there's an issue with the power curve of higher rated shield cells, or in other words maybe the top end units are recharging shields too fast. But from where I'm at, a mid range Cobra with around 1 million CR in upgrades, they seem perfectly fine and not OP at all.