1 LC and Prosper are the biggest but there are quite a few more.
2 I assume you mean apps for Android and IOS. LendingClub Automatique is the only one I use but it is a basic app and I can not invest through it. Dunno about others.
3 LC, for the most part, acquires loans and then sells them off. They can be sold off fully to lets say hedge funds or banks or broken up into pieces on the retail side for a min of $25. (We here are retailers.) These loans are not secured. While a borrower may be approved they still have to wait for their loan to be funded.
Borrowing
1 LC and Prosper use their own secret sauce to evaluate borrowers and how to assign a loan grade to them which determines their APR.
2 Here is the backtesting by states over the lifetime of LC and the amount of principle by state.
AK $47,584,500.00
AL $205,321,500.00
AR $118,529,625.00
AZ $371,420,125.00
CA $2,381,120,750.00
CO $350,937,700.00
CT $258,351,350.00
DC $44,626,375.00
DE $46,383,500.00
FL $1,086,367,700.00
GA $553,124,000.00
HI $86,665,625.00
IA $112,800.00
ID $9,916,200.00
IL $686,934,525.00
IN $262,838,725.00
KS $145,571,800.00
KY $154,921,250.00
LA $197,684,500.00
MA $404,969,000.00
MD $408,777,575.00
ME $20,671,325.00
MI $414,213,200.00
MN $289,381,725.00
MO $260,849,575.00
MS $79,442,625.00
MT $44,781,275.00
NC $461,983,950.00
ND $17,096,950.00
NE $33,225,900.00
NH $80,761,625.00
NJ $649,120,550.00
NM $92,970,725.00
NV $219,523,975.00
NY $1,357,315,850.00
OH $539,685,675.00
OK $153,868,200.00
OR $185,857,200.00
PA $568,585,500.00
RI $68,408,100.00
SC $202,084,000.00
SD $32,424,050.00
TN $249,754,925.00
TX $1,418,301,350.00
UT $115,040,250.00
VA $516,024,075.00
VT $32,543,800.00
WA $361,486,825.00
WI $211,008,375.00
WV $75,265,975.00
WY $39,240,175.00
3 Biggest obstacles?
http://www.lendingmemo.com/peer-lending-problems/For me, before I came here I had no idea what LC was/did. It is a steep learning curve on how it works and what mistakes not to make.
For LC, the ousting of their CEO shook the confidence in its investor base and is still trying to rebound from it. Quick Google search will net you many more issues.