This article shows that cheap SSDs are basically cheap USB sticks with a SATA connector attached.
Any run of the mill, entry level USB flash drive behaves the same way. Fast until caches fill, then limping while trying to write this data to the proper flash back end (at 10MB/sec in most cases).
If you pay the price, your USB drive will be a proper SSD with a USB to SATA controller, SMART and everything (Sandisk's Extreme Pro drives, for example).
Any run of the mill, entry level USB flash drive behaves the same way. Fast until caches fill, then limping while trying to write this data to the proper flash back end (at 10MB/sec in most cases).
If you pay the price, your USB drive will be a proper SSD with a USB to SATA controller, SMART and everything (Sandisk's Extreme Pro drives, for example).