1991/1992 (?)
I purchased one of these 3.5" drives and it worked fine for about 6/7 years - in fact it worked right up to the large sliding shelf that the 6128 Plus was sitting on snapped off (1999) smashing the Plus, Rombox and drive to the floor.
Link to SD Microsystems page in the Wiki:
http://www.cpcwiki.eu/index.php/SD_Microsystems (http://www.cpcwiki.eu/index.php/SD_Microsystems)
God that must have been a terrible day.
It effectively ended my CPC use for about 18 years, so yes it was grim - but over the last two years, with the help of Bryce (and a few others on the board) everything has been repaired and I'm back using these beautiful machines.
Just make sure you use sturdier shelves nowadays :D
This is the leaflet that came with the SD Microsystems Picture disc.
I was going to include this in the MicroDesign Plus thread as an example of some of the clip art available for the CPC but finally decided it should be here with the SD product list. As per that list, this would cost you £12.50 + p & p back in 1991/1992.