I too like "regular" flat pedals and regular shoes when riding. But I did find my foot would slip off the pedal fairly frequently, espec. when wet from wet grass, or when going uphill steeply. Very disconcerting. This bothered me enough to get some "PowerGrip" straps which I attached to my regular flat pedals:
http://powergrips.mrpbike.com/pg_benefits.shtml
Be sure to click on all the links there, it will show how they work.
I like them a lot, and they give me more security but I don't feel "trapped" in them either. You do have to practice a bit with turning your heel outwards AS you pull your foot back off the pedal, but it's pretty easy to get used to after a few practice times.

Another option is to ask the bike shop to adjust your new toe clips so that they are set loose and you can just slide your regular shoe in and out without tightening the strap each time. You'll get used to that too easily.

A third option is to have them put the flat pedals on there if you want them.