Simply put, LendingTree is a loan broker. Using their online process, they help borrowers find lenders willing to offer loans. At its best, their process should allow borrowers to find the best terms available from their partners. Unfortunately, the number of lenders participating in their programs are not unlimited. Borrowers are limited to their partners – for better or worse. Furthermore, their system could be "optimized" to find the best deal for lenders – not borrowers. Unless we know their system for matching, there is "some"risk they might not work in your best interest. To prevent this, shop around.
As loan brokers go, LendingTree does a good job. Just remember, every company that appears on their site paid them to be there.