Regular Shields vs. Phased Shields

[s_rat]

When you upgrade from regular shields to the first level of phased shields, I notice that there's quite a drop in the value of shielding provide by one unit.

Do phased shields also provide protection against unphased weapons, or should I be providing a mix of both shield types in my designs?

Or maybe I should mix both types when I'm at the top of the unphased tree and the bottom of the phased tree....and the gradually go to all phased shields as I get to higher levels?

And do shields provide any protection against DUCs? I'm assuming not, but I'm not sure.

Sorry for so many questions.