Props are great to liven up a presentation and make things more tangible for your audience; even if they can't actually touch the props you bring. If you are doing a product introduction or demo of sorts, I strongly recommend to bring your product with you, if it fits on the stage somehow. Seeing a real person interacting with it, holding it, or simply standing next to it (if it's really big) will give your audience a much better idea of the size and use than any product photo on a slide could do. So if the goal of your presentation is to introduce and eventually sell a product, this should be a no-brainer.
If you still need convincing, watch Steve Jobs introduce the MacBook Air (remember the manila envelope?) or, a personal favourite of mine, the iPod nano:
Ever wondered what this pocket is for?