We think the returns are excellent, "on an APR basis" as you said, which is another thing we need to communicate better. A 10% return in 6 months is kind of the same as a 5% return in 3 months, both of which are 20% in a year which is great. We don't think APR really captures this idea correctly though and may want to instead come up with some similar metric that will allow you to better compare the offerings.
We also need to better communicate the backers' responsibilities in that promoting isn't exactly optional. This is a similar transaction as buying goods on Ali Baba then putting them up for sale on Amazon and Ebay. If you do that but don't do any marketing, you can't have an expectation of profit. Some goods may sell naturally, and especially with the help of the other backers, but you should do your part to help with the marketing.