It's fine, it won't be of particular usefulness as far as admissions goes, but it may be marginally useful in the course depending on what you do specifically in it. However bear in mind all engineering degrees are primarily courses in the principles of engineering science, and the design elements of them are not always the same as you might find in a product design course (for example the creative aspects of design are not what engineering design refers to; engineering design refers to using the iterative process of design with the theoretical concepts you have learned to plan some system out).
I would note no university will expect you to take more than 3 A-levels and offers are normally made on the basis of 3 A-levels, so if you are struggling with the workload I would suggest dropping something, and of your subjects product design will be the least useful while on the course and is not really relevant for admissions so it would really be that or the EPQ. A-level FM will be much more useful on any engineering degree than product design once you are starting the course.