I feel that the reconsideration letter is still useful. It doesn't necessarily affect the grade directly at senior examiner, but it can make the local examination institution (e.g. BC) speed up the reconsideration procedure (mailing and notification)
Handwriting is a no-no, no matter how good your handwriting is. Format, just write it as a complaint email. Print out the full text, and then sign it by hand. The title is optional, and the title at the beginning of the text (e.g. Dear Sir/Madam) and the tribute at the end of the text (e.g. Yours truly) should be included. In terms of content, the statement should be polite and restrained, and the tone should be to the point and not exaggerated.