I have invested in 15 companies through Kickfurther, starting about a year ago. Five have been paid back completely, and the rest are still in payback phase. The ones that have paid back have earned between 10-17% APY.
The idea with Kickfurther is that your loan is secured by the inventory. So if the person doesn't pay you back you end up with inventory that you can sell on your own to recoup cost. Since all mine so far have paid back, I haven't had to test this step. But I did have one company that initially had a problem with their inventory (the factory created faulty product) and it made me realize that although they say it's secured by inventory, if the inventory isn't actually created, then you have no collateral.
Some of the companies have been great to work with (ie, great communication, payback exactly as promised) and others have been frustrating (ie, poor communication, late payments).
But overall, it's been enjoyable and a fun way to diversify. Whether it's truly worth the risk is up to you. If you can find companies that have already proven they can payback (some have used Kickfurther multiple times to expand their inventorY), then those are likely a more secure investment.
fyi, I used Kickfurther to earn rewards and meet minimum spends on credit cards, so I am getting a higher return than the regular APY listed above. Kickfurther tries to encourage people to fund with ACH rather than credit cards by offering an additional 1-2% on your money transferred to Kickfurther. They are currently running a "holiday special" now for 2% on ACH transfers to Kickfurther. You do lose 1.5% when you transfer money out of kickfurther, but you can reinvest earnings rather than withdrawing and just keep it earning there if you like. And Kickfurther tells me they don't report any earning to the IRS. I imagine that might change in the future though.