The strap harness is a great choice if your kitty is a bit of an escape artist - they aren't as pretty as the step-in harness, but they're much harder to slither out of. The low profile also makes it great for introducing cats to harness training, because they can groom and move more easily.
As with any harness, I strongly recommend taking the time to get your kitty used to the harness before you take her outside for the first time, because kitties are experts at getting out of positions they don't want to be in.
Let her wear it around the house for a bit to get used to it. Start with a few minutes a day, and gradually increase the time she spends in it as she gets more comfortable. Encourage your kitty to eat, play, and groom while wearing the harness, because that'll help her accept that it's not so scary after all. Harness training is a process, so don't rush her! Good things take time, right?