Yep, I'm a real fake doctor. It's up to you really, I wouldn't use the white strips because you pay about $50 for a box. If you get the trays (an upfront cost of maybe $300, including your first few tubes of gel), and you want some more down the road, the refills are actually less than buying the white strips. So you're getting professional strength trays that are customized to your teeth (so they work better), which don't peel off, and also cover more than just your front six teeth (if you have a bigger smile this is important) all for less than the cost of white strips. And they can give you different percentages so they could give you a lower percentage for your bottom trays so your teeth wouldn't be so sensitive and a higher percentage for your upper trays. To me the upfront cost of the trays are worth it. Otherwise, it's a personal preference on crest vs listerine...in your case, if you're happy with it, stick with the listerine.