Thanks all for the info. It helps.
Re: #2. It's more likely I'm missing something. My concern with larks heading the fixed loop to the strap is sometimes I end up with two trees that are closer together than one would like. I end up using a marlin hitch and a biner (descending loops Garda hitch suspension) do I'm imagining that the buckle would replace the marlin hitch in those situations. Or would the whoopie sling be able to shorten up dramatically. Sorry if it doesn't make sense as I'm trying to imagine it with limited experience with whoppie slings.