Mr.Aerial
The big steel biner is used for arial steel work mostly. The gate is large so it can fit around angle iron. In the tree industry I use it for rigging attachments on the ground. I haven't been in the industry long but the lowering device you got on ebay was over priced
sorry Its been outdated by the portawrap. Get a sherill catalog it will have what you need for tree work. My idea would be to put that fall arest stuff, the rope grab (its not the style of rope grab you want) the lowering device and put it on ebay to make up $.
keep the biners