Traders are better off NOT using documents like LOI, ICPO, FCO, etc. Even if and when they rarely are used in internal trades, on a restricted level within specific industries, they have no legal or customary basis in International Trade whatsoever. In fact the presence of many of these terms are considered to be signs of Advance Fee Fraud, by knowledgeable players and law enforcement.
There are a lot of very important items in these documents and you do not want to make a mistake here. This begs the question, "What is the most important clause to include in a purchase agreement or letter of intent?"