So basically, they are taking something like a SATA-II (or maybe SATA-III) SSD and putting in an external USB3 enclosure. I've already been doing this for myself as I upgrade my SSDs. SATA-III is faster than USB3, so it's somewhat of a waste. But seeing as most drives are SATA-III now and they are still under <$1/GB, it doesn't make much sense to use older SATA-II drives. That being said, using the SK Hynix SSDs, which are incredibly cheap AND towards the top of the performance charts, you build yourself an enclosure much cheaper.
As other people have commented, this isn't any spectacular deal in that you can DIY for considerably less. Given that there are "tool-less" enclosures, even "mom & dad" could figure out how to make one work without much effort.