These things have worked very well for me. Especially when I used to be a pot head years ago and I encountered police regularly. Now that I'm not doing anything wrong I don't get stopped as often. Now if I talk to police it's mostly about security work we're doing, a house we're hitting or something.
Just one thing to add. Assume that the cop is tired from working a long shift after having worked his other job earlier that day and be super polite as you refuse. You don't want to come across as "an uncooperative SOB", but as a nice guy who knows his rights. Say something like "I'm sorry but I really need to get going so I can't consent to a search right now." Cops are people first and foremost and like all people they'll generally be nice to someone who is nice to them first. If you're an asshole to them, they will often respond in kind.
I once ran right through a red light right in front of a cop. I was out of state and didn't have my license or insurance with me. To top it all off, I was carrying a pistol. He let me go without even a written warning! Partly this was because I treated him with the same courtesy a I treat a customer. So refuse the search, but do it very politely.
Also watch for "you don't mind if I take a quick look back here" as they open the door. "You don't mind" is always a question and the answer is "I'd rather you not. I can't consent to that." Unless of course I am the one doing the searching.
