Sorry but I think its totally UNETHICAL for a company to ask someone to re-design part of their product for free. Seriously, would you ask a lawyer to argue a part of your case before hiring them, or get an accountant to figure out 2 pages of your taxes for free? As creatives in this field its time to put a stop to this thinking that we can work for free on a companies product. There plenty of design challenges that can be used to determine how someone thinks. This is a big red flag about how the company/founders think.