I don't know that particular brand of pedal, but see if it has an adjustment for the tension and make it as loose as it will go. You have to practice in a doorway first, just to have confidence that they will unclip for you. Then it's just practice. And think about them before you stop. I don't think it matters where in the stroke you clip out, you'll get your own technique. If they continue to frustrate you, hopefully you can discuss it with the folks at the bike store. They should be willing to swap them for another brand. There should be an adjustment for the tension. Also there should be a lot of discussions about them in the forum, with a lot of good ideas on how to get used to them. Try a search across the various forums.

I've never gotten real comfortable with them, but most people seem to get used to them easily enough. I have one bike with regular pedals and the half-toe clips, which I like. I have a road bike with clipless pedals, and it was in the shop for a while so I'm out of practice. I have to think about stopping, and clip out on the right ahead of time. I have knee issues so I may stick with them and get used to them again. I may also swap the right pedal with the half-toe clip. It'll look odd, but who cares. The main reason to use them is to keep your knee tracking correctly, in my opinion. And you can pull up on the up-stroke. But if I wasn't concerned about my knee I wouldn't use them. I'm probably in the minority here. :-)