I recently got big dots installed on my Shield 9. Having never shot a "dot the i" sight picture before, the learning curve for me was pretty steep. I would have thought it would have been pretty simple, but it honestly took me about 100 rounds to become even remotely "acceptable" shooting with them. The target acquisition could be really quick with that big ol front sight, but due to the fact that I was attempting to learn how to shoot with them from a basic level, I never really tested fast follow up shots and multiple targets.
On a side not, my shield is out of commission at the moment, and I place a bit of blame on both my gunsmith and XS. After that 100 rounds, and a day of carry, I noticed the front sight drifted all the way to the right of the slide. I popped it off and low and behold there was no adhesive used to hold the sight in place on the slide (The sight package includes red Loctite). After I call to my gunsmith and some digging around the internet, I learned that... a) my gunsmith deemed it unnecessary to use adhesive on a dovetail sight, and b) the dimensions and quality control on the specs of the front sight are sub par. I understand including the Loctite in the package, and I also know it should have been used (I was quite upset to find that it wasn't)... but on the other hand, there was no filing done to the bottom of the big dot front sight, and still it slid right off the slide.
Some things to consider. Understand that there may or may not be a learning curve for you with the big dots, and that it can be frustrating. And if you go with this sight system, Loctite the **** out of that front sight and keep an eye on it to ensure it hasn't moved with time.