I have the XO shifters and they work great. There is a larger thumb paddle for down shifting and a smaller one forward of it for upshifts. It really did not take much time to get used to using them instead of the Shimano shifters. My bike came with the SRAM grip shifters, but I found the trigger shifters a lot easier to use for my small hands.
BTW (thinking of your other post re: bikes on Ebay), I got my Racer X on Ebay and had no problems. I think it is important to query the seller and see how they respond, ask questions, check feedback. This was the largest purchase I have ever made and I was nervous about it, too, but I got a good deal and everything went super smooth.