I know the work I did would've been a strong proposal for my current employer and likely would be the course of action we'd take. Similar to other reviews I've seen, however, the work I did didn't factor into the the hiring panel's decision - past experience had - and I would've preferred not to have done hours of work on my personal time when I could have been told this prior. This could've been avoided by simply not having me do the assignment. I'd still expect to complete some form of exercise for any similar interview and honestly enjoyed the problem set - it was a great set of questions - but I'd rather the team were more considerate of my time up front.