I tried it, briefly, a few years ago on the Taff ... you may well have been there Kieron (?) ... a freezing cold January day at Taffs Wells when there was a little lad who was wading in jeans?

Anyway, Stef' Jones had some and I tried it. I wasn't overly impressed by its floatability but it was good that you could mold a small amount around a knot and produce a very effective 'sighter', and have something not so bulky as many 'indicators' are.
Something I use is a tape produced by Tiemco that simply rolls onto the leader. I've not seen it advertised for a long while, the last time I found any was in Bled, Slovenia. It used to come on a roll holder with a little serated edge cutter. I think Tiemco do something similar now with pre-cut sections on litle sheets.