I also don't think it is appropriate for a pharmacist and may actually end up intefering with the good service he provides. I find the content overly personal, intrusive, even the idea of giving a personal letter to a phamacist. I would encourage you to remember how your damaged relationships previously with invading the personal space of other professionals. Hope, there is no way that sort of approach is ever going to serve you well even if the actual content of what you say to them seems positive. Your decision of course but since you are asking for feedback, mine is that I would not give him the letter or would approach him in any other way except what his work involves. Maybe I would express in a few words when I see him in the pharmacy that I appreciate his service, but that would be it.