I do not mind leaving my coins on freebitco, and as you said, the interest can give us additional income, although it will depend on the amount we deposit. But on the other side, I will not let myself to store my coins on that site because the risk will be too big. But for freebitco, I trust the site and I believe that the site will not run away. Besides that, freebitco has good reputation among the other site.
No matter how trustworthy they are, I will never keep my coins in freebitco, or in any other sites. Trust doesn't matter much in the Bitcoin sector. Back in 2012-13, Mt Gox was regarded as the most trustworthy cryptocurrency exchange. But what happened after that? You never know when these sites will go down, irrespective of their good reputation and trustworthiness.