... everything is based on context of the application. This is barring intentional or accidental dislocations, sprains, eyes and groin shots, and bruises. To put a postive slant on this...
Rubber trainers are good for hard sparring since they do almost no bodily damage if the body contact is incidental.
Wood trainers are good for choreographed drills and disarms. To some degree they are good for free flow drils. Because they are stiff, they are good for practicing self defense especially. They are good for progressive step drills.
Aluminum trainers are great for drills and disarms, also. The added realism in the feel of metal against skin is the advantage of using such a trainer versus other materials. The feel of it mimics what metal from a real knife would be like pressed against the skin.
As for all the production companies that make trainers, they are good for practicing realism in deploying and switching grip positions of a knife. They, also, have the balance to a real knife since it mimics the configuration, lines, materials, mechanism, and weight the closest. They are just as susceptible to damage if used hard and can hurt the individuals using it if they happen to break apart. Even safety edges of trainers can become hazardously sharp or gouged if it is metal on metal contact with something else, like another trainer as an example. Hitting or dropping them on concrete or any other surface that could damage them.
Short of full out sparring, I think all trainers have their merit. Even I have a bias as to what I would use. Shop and compare. To take Chuck's response a little further, I would add that you get what you pay for. You pay a lot to get a lot - you pay a little to get little. You can either go for options / bells and whistles or you can go for something really basic. It's all up to you.
Originally posted by Gollnick
Do a websearch for a company called I and I Sports.
But, be aware that their cheapie trainers are junk.
Rubber trainers are horrible. They don't double a live blade at all and they're easily broken.
Wood trainers are horrible. They get splinters when they knock together and then you get slinters in your hands and arms.
Aluminum trainers are horrible. They get nicks in them when they bang together and pretty soon what you have is essentially a serrated edge.
Benchmade, Spyderco, Emerson, Timberline, and maybe MOD and/or Microtech make the good stuff. If you're serious about training, don't waste your money on the cheapies.
It's one of those things where, as the old commercial used to say, "You can pay me now... or you can pay me later."