I think some confusion has arisen in the use of the BIAB as a boil filter, as well as a mash liner. The BIAB folks state on their website that both uses work well. Personally, I line my mash tun with a 400 micron bag whenever I am mashing and regardless of whether I am recirculating or batch sparging. I also occasionally use the bag (whether 400 micron or 200 micron) as a hop spider substitute to allow for more free flow of hop pellets in the boil. Clean up is pretty easy with the bag, but it does represent an additional item that must be rinsed out (twice if using the same bag for both mash and boil filter). The key is that any heat source must be avoided by suspending the bag above the bottom of the kettle or mash tun. The mash tuns I have all incorporate a false bottom or basket insert, so those are fine; as to the boil, I just clamp it to the kettle such that the bottom of the bag is above the bottom of the kettle. Easy peasy. Cheers!