Pros
I am currently an engineer at Prosper. I will speak mostly of the engineering/product/ops/finance side of the business, because that's what I know. Prosper has two great financial products. On the one hand, we lend money for unsecured loans at far better rates than banks or credit card companies. On the other hand, we offer investors a truly superior fixed income product, with stock-like returns but bond-like volatility. Banks' spread is like this (picture my arms extended fully); our spread is like this (picture my hands maybe a foot away from each other). We are more efficient than banks, less greedy, hungrier, faster-moving, and less lazy. They are ripe for disruption, and we will disrupt them. Lending Club's problems allowed us to leapfrog them into the #1 position in this fast-growing space, which is still only a tiny fraction of what it could be. The potential market for Prosper is huge, because for better or for worse, consumer debt in the US is ginormous. When I first arrived at Prosper, there were some folks in product, engineering, and ops who didn't want to be here, or didn't care enough about the company to do a good job. Most of these folks are now gone. Some of them have written vitriolic reviews of Prosper on glassdoor. Every month, things get better. We have a lot of seasoned industry folks making methodical, strategic decisions, and we have a fast, startup-like pace, and the engineers are herded by (in my experience) really good product people. At this point, I am able to spend a significant portion of my time here doing actual engineering, more so than when I joined the company, and more so than at most places I've ever worked. And as I look around, I see teams full of really smart people. And respectful, and nice, and (dare I say) somewhat mature. There's not a lot of shenanigans, but there are a lot of interesting people, and there's diversity and respect. And the life/work balance seems quite good--almost like at a non-tech company! If you are good at what you do, there is a lot of potential for you at Prosper. If you're not good, or you don't care, or you have a low tolerance for change, or you just want to punch the clock, then do me a favor and go somewhere else. As for the "Recommend to a Friend" question? I've already referred two.
Cons
If you want something completely predictable in a mature space, this may not be for you. (But you may be missing out on some potential upside.)