I can only speak for myself, but I don't like doing transfers - they need ages to dry, you need additional wax paper or the like (which means an extra expense), extra storage room... so I only do transfers if there is no other option.
For the cookies you plan there definitely is a much easier way. Flood your cookies and let them dry completely (no color bleed risk then). Make a template of the letter (e.g. with cardboard), trace thee outline onto the cookie with your scribe tool or an edible marker, outline in white (let the outline dry to minimize risk of color bleed), and fill with red icing.
The only reason I would consider tranfer letters for them is that you can achieve a cool effect if you place the transfers onto the wed flood icing. They sink in a little then which looks rather neat 