Is the Rival gruppo worth the extra $$? I heard the Apex is just as good but it's just heavier... Is the Apex comparable to a Shimano 105 group?

I keep hearing that too. That means that Apex is just as good as Red because that line of thinking goes all the way up the line.

I find it hard to believe.

I road several Apex and Rival equipped bikes when shopping for a new bike. I didn't expect to be able to tell the difference between them, but subjectively, riding one after the other, I felt the Rival was more precise. I can't tell you if it was the shifters or the derailleurs, or something else on the bikes, but something made the Apex feel less impressive than the Rival. For me, it's worth extra $$.

Does Apex have front shifting zero loss?

^ Yes. https://www.sram.com/sram/road/produc...letap-controls