These streamers typically are very light with great movement and very effective presented in shallow water to spooky fish. I have been tying and using them for years. Try tying one in the color of a ISO nymph on a #10 or #12 2X long hook and strip it erratically in the shallows. Hang on! As Karstoppo indicates they are very effective in the salt (shallow spooky reds and sea trout) for the same reasons stated above. Thin stem marabou works best when tying.
These streamers just sort of hover on the pause and little currents in the water pulse and move the marabou. Weighted patterns tend to sink on the pause and present differently. Gartside soft hackle streamers naturally take on a baitfish shape when in the water and aren’t the puffy feather balls you see when freshly tied and aren’t the thin collapsed bit of material you see when wet, but out of the water. They only look right when stripped, paused and drifted in the water, the only place they should look or need to look right or fishy.
The only drawback is that they don’t hold up well to sharp teeth. They do about as well as a deer hair clouser under attack from sharp toothed predator fish. Gluing or putting on a head or encasing them in glue armor would defeat the purpose and goodness of the pattern.
I caught my first fish on a homemade streamer using this fly. At the time I didn't even know it was a pattern, I just lashed on some marabou and a mallard flank collar and it looked good enough, and caught lots of fish.
In my opinion, one of the most innovative tyers ever. Variations of his flies have been promoted by many current tyers as their own creation without giving any recognition to Mr Gartside's original design. Typical
Alas the notion of intellectual property rights has not made it to fly tying... But it is a very slippery slope. How many of the flies we tie are wholely our own? I have learned from so many of greats...
I agree, most of the flies I tie for myself are variations of another pattern or of some other tyer's technique. What I find annoying are people who promote their flies as original ideas as part of their personal marketing strategy without acknowledging any credit to the original tyer. Oh well.