The SRAM double tap is different from Shimano in that you do both the down shift to an easier gear and up shift to a harder gear with the small lever under the large brake lever. Push the lever in half way and you go to a higher gear. Push it in all the way to drop down in gearing. With Shimano, of course, the two shiftings are done on separate levers.
My problem was SRAM road shifters was getting that lever pushed all the way in when I needed to drop down in gear, as when tacking a big hill. Had to reach in too far for me to do it, easily. Had to loosen my grip on the hoods (and I don't have petite hands) to get it done. Very awkward. Then, if I failed to push the lever in all the way or released it before the shift was complete (the Apex was very slow), I'd end up shifting up a gear, instead of dropping down a gear. ARRGGHH! That, of course, stopped my climb in its tracks. It also made my Salsa Fargo worthless for trail riding where shifting needs to be even faster and the timing more critical. Was a total disaster for techy trail work, even though Salsa advertises the Fargo as a drop bar mountain bike. Not for this gal!
Also, I wore out the Apex shifter on the right side in one season. My bike shop took care to it for me, but even repaired, they couldn't keep it shifting, right. Lots of trips back to the shop. This same shop now refuses to stock any bikes with Apex because other customers were having the same problems. When they do stock SRAM road group, now, their minimum is Rival.
I found down shifting on the Shimano by pushing the brake lever in to be much easier and much faster and much more comfortable, all with my hands firmly on the hoods. I have used 105 for some moderately techy trail work and while not as good as MTB trigger shifters, of course, it does work.
Again, I love SRAM MTB shifters - use them on several bikes - but SRAM road shifting doesn't work for me. Does work for other folks, just not for me. Hope I haven't offended any SRAM road fans. You'll have to try it and decide for yourself. You may like it, you may not. Not putting it down. I just couldn't manage it, well. Bad choice for me.
If anyone does go SRAM road, though, I'd highly recommend stepping up to Rival.