They differentiate themselves by offering SSDs for all instance sizes + offering a very cheap level ($5). While SSDs won't improve all workloads, I think "high performance" claims compared to the typically IO-weak alternative isn't unreasonable.
Also, they're popular enough now that I'm surprised people haven't heard about them (especially after recent funding)...
Yes, at least. For one I believe all DigitalOcean boxes have SSDs. I've found their boxes much better per $ than an EC2 VM. EC2 has a much wider tool suite and is possibly better if you regularly spin machines up and down. YMMV, but for just 'a box' they compete pretty well IMHO.
Also, they're popular enough now that I'm surprised people haven't heard about them (especially after recent funding)...