Ah yes. "The Bung" in British stillwater trout fishing; strike-indicator fishing on rivers in the States and here.
Mixed feelings about it. I have used the method since the late 1980s, when it was introduced to me by some extraordinary Austrian river fishers, "pioneered" it in far-off South America with nymph for sea-trout (at a time when everybody else was still hurling and stripping black Woolly B*gger streamers), taking fish of well into the 20s of pounds, used it (with styrene / cork / foam / yarn indicators) with great success for trout and grayling all over the shop including here, but............
People become "hooked" on the method, end up being one-trick pony floatfishermen totally incapable of fishing the nymph both upstream and downstream and detecting takes from fish without the aid of an indicator, cease to be functioning flyfishers.
I seldom use the method now.