Never used one, but I am leary of anything that doesn't allow for chassis flex. The stock coupler has some in and out allowance that a straight up u-joint doesn't give.
There are sliding sections of shaft available and is the direction I plan to go if I go down the road of deleting the stock coupler.
The main issue i can see with the coupler is that its quite bulky and touches the pipes, a manual steering column would be lot better as coupler obviously much closer to the steering box.
By sliding sections of shaft do you mean you essentially making the shaft longer so no adapters required? Do you have a link to the items?