Just to add a little more info here, Phil is correct, if you don't get the proper helical couplers for YOUR specific needs, it will not hold up, but that really should go without saying as you must choose any coupler for your specific application. It's not a "one size fits all" kind of thing.
I do also like Bowbers idea of "oldham" type couplers as well as those are great too. Again, though, you have to figure out what your specific needs are.
When ordering any coupler, they give you the specs of the particular coupler that you need, such as torque rating and misalignment data as well.
Hope that helps a bit more.
Dave