I'd pick 'Do both simultaneously' - in my experience, it's tough to get market feedback on a product that doesn't exist yet, but also, delays in launch can mean missed opportunities; how do you see the costs balancing out?

I'd pick 'Do both simultaneously' - in my experience, it's tough to get market feedback if your product isn't ready, but you also can't refine your product without user insights. How do you plan to resource both efforts?

I'd pick 'Develop a solid product first' - but how do you define 'solid' in this context, and what are the key milestones to hit before moving on to marketing?