That's exactly how it was for the studio based series - the expert wasn't there to "guide", but dictate the design. On the roadshow and last series based on the roadshow format, however, it was entirely down to the teams to design their own device. We had to submit our plans to the production team for approval prior to the start, in what sounds like a similar process to GMRC. You also had to supply our own scrap! Any "safety" mods were done on the morning of the day of the competition.