I use Jet on a regular basis. I try to avoid Amazon wherever possible, they're good but they have too much power so I try to help any alternative. Their selection isn't as good as Amazon, but usually it arrives quicker. Books are not quick, but cheaper than BN (even though BN ships them)
They must be burning lots of cash though. I placed a $100 order with about 7 items and it came in 6 different boxes.