The best UI is no UI at all.

I can't think of a single time I've looked at a product tour and thought "well, I'm really glad they told me that, I never would have figured that out.

What the product tour I think often misses is that people don't want to learn your entire tool at one time.

They came to do one thing, that one thing needs to be brain dead simple.

Over time, you can show people what else they can do. But a product tour isn't the way to do that.

I think progressive UIs where you expose more and more to the user over time is the way to go.

If you're thinking "but I have so many features and capabilities this person needs" you probably haven't identified what the one thing people are paying you for is.