I have used them quite a bit over the last 5-10 years. Sometimes they outproduce a traditional crawler harness....sometimes they don't.
A couple years ago they came out with a "Super" slow death hook that you can use a whole crawler on. A friend of mine uses soft plastics instead of a crawler and has done pretty well on walleyes, smallmouth and pike using that method.
I received a few sample slow death hooks and trolled them slowly behind a 3-way. No harness. Just straight leader to the hook and caught some nice walleyes out at West Branch this way. Don't know that they're a staple, but definitely worth a go!
I haven't personally tried them yet, but Trokar makes the Re-volv hook, which from the reviews i've read is infinitely better than the slow death hooks. Going to place an order for some soon and I'll report back.
Basically all I use anymore. I mainly fish for saugeye but I believe they are better than traditional 2 hook rigs. Added action plus I believe it’s harder for smaller junk/ non-target fish from robbing you. Reel in plenty of gills with them but atleast your not standing there wondering if you have a worm left.