I'll second Bambodoggy's caution about using these things in British waters. I'm not absolutely certain, but I'm pretty sure that the use of this type of spring loaded hook is illegal in any circumstance. I am certain that to leave them to fish for themselves (as they were designed to be used) IS most definitely illegal in the UK. Used in this manner they would be considered to be "Set Lines" or "Night Lines" and you would be leaving yourself open to prosecution and a pretty hefty fine (and criminal record) if found using them.
As a survival tool they no-doubt have their uses, but as with so many techniques and methods that might be of real use if you were in a desperate, life-or-death survival situation, you are unable to practice "just in case" within the UK without falling foul of the law.
If you have permission to fish the waters you are using, and the method is allowed, I'd stick to ledgering a worm for trout. Fishing for trout is often so easy with bait that it is mostly considered "unsporting". This is why the art of fly fishing was developed. Not because it is the best way to catch trout, but because it is a more "sporting" option than offering them a juicy worm that they can hardly ever resist.