What is the glass package they are offering you? Argon will get you a better insulating value. So I would say it is a definite help. Most residential companies really offer it as a standard these days.

Materials sheet says laminated insulated. Glass makeup LIA207AA5. Glass 7/8” LIG (1/8 AN - 7/16 AIR - 5/16 AN/AN). PVB090 interlayer.

Windows are rated for, among other things, U-factor and Solar Heat Gain Coefficient (SHGC).

In cooling dominated climates SHGC is the more important of the two, that's why a low solar heat gain LowE coating is recommended (often mandated) for that climate, because the coating blocks direct solar gain helping to keep the inside cooler. Coatings also improve U-factor over clear glass as well. While argon gas between the lites does nothing to affect solar heat gain, it does improve U-factor about 8% over an air-filled space.

If it's a costly upgrade (shouldn't be), then let it go. If it's free (should be) or minimal cost for the upgrade, then go for it.

What he said....but seriously, should be close to standard now.

It isn’t free. The solar gear gain coefficient for the PGT configuration is .2200 for a 36x62 window.

Is the U factor more important in hotter climates?

More important in colder climates to be honest. But they are important anywhere you are going to have a large temp differential across a surface.