Props in seminar

The goal of your seminar is to educate and inform your audience about your work. If showing the audience a prototype of your work will help them to better visualize and conceptualize what you are doing, then why wouldn't you want to take advantage of that during your talk?

So long as you properly integrate into your talk—make it an essential part of it, rather than just "for show" while you talk—then the prop will do its duty.

What you might want to consider is taking some high-quality photos of the prototype that you can show on the screen as you talk about the prototype while holding it. Then you can get the best of both worlds.

This is a terrific idea, and moreover you should also strongly consider passing the device around so that people can inspect it and hold it in their hands. The idea that the opportunity to have either visual or tactile contact with a scientific instrument or device "doesn't add any content" is simply false. At the very least, including a prop of this sort in your presentation will add an unusual and memorable element to your talk that would set it apart from the hundreds of other talks that come and go in a university department and are easily forgotten; at best, the prop will actually give the seminar participants some actual insight into your experiment and the related science. Either way, it can only work to your benefit.

As a small illustration, I recently brought some 3D-printed objects to a math seminar I was giving. Although one can make the same argument that showing pictures of the objects (which I also did) would contain exactly the same information as you could get from handling the 3D models, the psychological effect of being able to handle the 3D objects, and the reactions I got, were both very positive.

Personally, I've always been unable to clearly understand the arrangement of a complex device from pictures or drawings, and I much appreciate the possibility of observing directly a device after its description.

In addition, since you've been invited to talk specifically about this device, the audience should appreciate your idea of bringing it along.

Therefore, yes, I think it's a good idea.