If the person reviewing the toy is of the opposite sex, but used the toy with someone of my sex, and can give input from that perspective, then I'm all for it.
If the person reviewing is of the opposite sex, and has used it on themselves, then it still depends. If we're talking about an insertable vaginal toy, the opposite sex has no vagina, and I don't feel that they can give me a good idea of whether or not it will work for a vagina.
However, if a member of the opposite sex is reviewing something like restraints or an external vibrator, I've no issue. I really think it all just depends on the toy and the way it is used as to whether or not a review will be useful.