The Banana Tree is a very reputable company. They've been around since 1955. Their website is
http://www.banana-tree.com.
I purchased my very first banana corms from them about 20 years ago—a Valery and a Cuban Red Dwarf. I still have descendants of the Valery. The Cuban Red Dwarf died due to frost. Both corms were large, between baseball and softball size.
In the intervening years I have purchased numerous seeds and corms from them, most recently some heliconia corms. One of the corms was slightly damaged and rotted soon after planting since the heliconia are very sensitive to rot. I contacted them and the corm was replaced immediately, at no charge, with the replacement sent via Priority Mail. I would not hesitate to recommend them.