It depends on what you mean by "safe." If you mean safe from the company absconding with the money in your account, never to be heard from again, then most likely, yes, it will be safe.
If you mean safe from loss on your investments/loans, then absolutely not. Peer-to-Peer (P2P) lenders like Lending Club, Prosper, etc. offer a way to access fixed income and potentially get a pretty nice return on your money. But it is not without risk.
You are essentially deciding whether to loan someone money, and that someone is a person you have never met (and likely will never meet) who has submitted an application through the P2P site. So, the only information you have is the information they provide along with a credit score - basically, similar information to what banks use when they are deciding whether to lend.
Each loan usually stipulates what it will be used for (e.g. debt consolidation, small business, car, etc) and it graded. It will also tell you what the interest rate will be. The higher the rate, the riskier the loan; the lower the rate, the less risky the loan...in theory. Most require a minimum of $25 to be invested in a loan - you can invest more, but it is also wide to spread your money out, just like in the stock market.
However, any loan (even the A-rated ones) can be late and/or default at any time, which will negatively impact your long-term return. So, you can build a well diversified portfolio of loans that range in interest rates from about 6.0% all the way up to 22% or 23%. However, that does not mean that you will get fully paid on all of the loans, and even the sites tell you that it is likely that at least one loan you invest in will default. That is just the nature of the game.
There is currently nowhere right now that you can expect a 6%+ return without any risk, and P2P lending sites are no exception. So, while I think they are fine to look into, like with any investment, I would not let it account for too much of your total portfolio, and I would not invest more into the loans than you could afford to lose. Chances are, you won't lose it all, but there are no guarantees.
Best of luck.
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