the WD passports are exactly what you are suggesting you will make. they are 2.5" laptop drives with a small sata to usb adapter. if you are going to carry them around i would go and buy a 128GB jump drive and just use that. or smaller if you dont need that much space.
As far as performance, no, but most or all current WD 2.5" externals contain a drive with electronics made specifically for USB, meaning there is no separate SATA-USB adapter board. IOW the drive cannot be removed from the enclosure and plugged into a SATA port.