JFYI, there is a newish little enclosure with Write Protection switch that sells for around 20 US$.
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it seems like very nice ) , and could be IMHO a good alternative/starting point for students (see)
http//www.forensicfocus.com/Forums/viewtopic/t=8713/
http//www.forensicfocus.com/Forums/viewtopic/t=10557/
and amateurs besides - if it behaves properly - an el-cheaper tool for the pros.
Particularly, given it's inexpensiveness, it may be a good way (somehow locking the switch to write protect) to give back to a less experienced user a drive containing a copy of evidence or recovered files, making them slightly more safe against accidental writes.
jaclaz