Quick link to a post by Mr. Keating about counterfeit Stingers from China.  As usual, quality counts, and it can cost more.  I sometimes buy inexpensive training tools so that I can experiment with them (especially when I know that they're going to be abused or destroyed in the process).  But I'm not afraid to spend on my carry gear, whether it's flashlights, batons, knives, holsters, or firearms.  What's your health, safety, & well-being worth?
I’ve been playing with some Karambit techniques for the past year or two.  I finally picked up an inexpensive model from United Cutlery to practice with after talking to guy at one of Pete Kautz’s “Seeking the Path” events a few years ago.  Since I just wanted to dabble and I wasn’t planning on carrying it, it’s hard to beat for $12. 
Then I made a wooden trainer so I could practice with a partner without fear of laceration.  The wood’s not as forgiving as a high-density foam trainer, but I’ve used wooden trainers for years with great success. A little sanding and shaping, maybe a little duct tape to prevent splinters and you’re good to go.  
My most recent purchase was the Boker Plus “Batman”. For years I have been keeping my eyes open for a reasonably priced Spyderco Civilian, but gave up hope and dropped $30 instead on something that I could easily pocket carry, but still use for Karambit-type techniques.  The only two drawbacks I see with the Batman are that it’s fairly bulky and the clip attaches low on the handle.  This means that it’s fairly obvious and sticks out of the pocket more than I prefer.  
Now I use each of the devices to practice a 35-step kata that covers a range of blocks, strikes, slashes, punches, and hooks.  Both left and right hand, as well as holding the knife in a forward or reverse grip. It’s interesting to see how the application of the technique changes slightly depending on the blade orientation, but using the kata as a conceptual starting point, the movements can be used with not only these hooked-blade
devices, but with straight blades or even empty handed.  As with most katas, there are a lot of things to discover under the hood, if you only take the time and broaden your

If you haven’t considered any of these kinds of curved implements before, pick one
up and give it a try.  Not only is it fun, it can also broaden your martial horizons.

Did you ever reach a point in your Kata where you made a mistake, stopped, slapped yourself in the head, and said (or thought) “I always screw-up this move!”?  Maybe it’s not a problem with your physical preparation, or your “remembering”, maybe it’s a hitch in your mental process.   When learning or re-learning or mentally rehearsing a technique, it’s critically important to Image Correct Responses.  As Asken et. al. put it: “When you mentally rehearse a response sloppily or incorrectly, you will perform it sloppily or incorrectly. It’s essential to not be sloppy, lazy, or incorrect in your images."  So when you see yourself practicing the kata, make sure you see yourself practicing it correctly.

I mentioned before how I like to use mental imagery in slow-motion to really lock into the form and execution of a technique.  The authors also state that it’s important to Image in Real Time.  Just like with physical practice, sometimes (many times) you need to
practice at game speed.  Make sure to practice your mental rehearsal at actual speeds as well.