Yes you can still miss a beat, which can be easy to do, but thats a small price to pay when being able to regenerate all of your shields. I can currently kill an Elite Anaconda in an Eagle, only possible with shield cells (for me currently, and I challenge anyone to do it without). This says to me that they're pretty overpowered.
But if you miss it, and you lose your shields, shield cell banks do nothing to regenerate them.
As for the elite 'conda... you can do it without shield cell banks in an Eagle. It's not easy, but it's doable. You can make it easier with at least one railgun on there as well. Being able to switch flight assist on and off on the fly certainly helps as well for maintaining high angular velocity against him while still keeping your nose pointed at him. I've had a lot of experience in Eagles and it would be wise not to underestimate it's capabilities in the hands of a good pilot, shield cells or not. I only have one shield cell bank on mine but I rarely dock without a few charges left. It's very light and easily outturns everything else out there except Federal F64s, which are so squishy you probably won't need to turn for a second pass, just hit em hard on the first.
I'm not seeing it as OP. I've seen a lot of OP - Ishtars in EVE are OP right now, this shield cell bank hubbub isn't even on the same level as that problem. You put enough pressure on a pilot using them, and I'll guarantee he'll lose his cool and make a mistake, as long as you can keep your own. Shield cell banks do not a good pilot make, they just give him a few more hit points to delay his inevitable doom against a better pilot.
As an addendum, having a good shield generator is going to be worth more to a good pilot than having the ability to recharge it quickly. I think a lot of people are filling up with so many shield cell boosters because when you're fitting for combat, there's really nothing else worth putting in those internals and they might be under the impression they have to fill em up. I know if I'm in a Viper, fit for combat, I have a couple of empty internals to keep weight down, and just one SCB.