Incentive for a demo isn’t new. It might increase your demo rate but might also introduce some leads to the funnel that want the incentive more than they want to learn about your product. So my recommendation to you would be to share the incentive with qualified demos, a questionare is nice, but a qualified demo is pipeline.

How much you offer for the gift card depends on your offering and audience, but if you’re thinking about around 100$ a pop, perhaps invest in AirPods or equivalent instead (at $150). Getting an actual device in the mail is more appealing than a gift card