There is a lot of free information available on the internet about how to increase your sense of self and your self worth. By all means you should explore some of those options as well. These Love Letters are designed to give you a bit of extra support in a specific area of your life.
Also, when you financially invest in yourself (with any of these love letters or something else), you are saying to yourself, you are worthy to invest time and resources in.
And last but not least, Thank You, for supporting a small business. The world would be very different and a monotone place if there were no small businesses left.