Calfee's eccentric is sub-optimum, to be sure. Even with the refinements that have been made since the first ones, it remains a problematic design for several different types of bottom brackets.
Any of these eccentrics that use compression are fine so long as you are using the newer types of cranks with integrated axles and either outboard to BB30 type bearings. However, they will all be problematic if they are used with a square taper, ISIS or Octalink BB, i.e., they are not backwards compatible. It's just a data point, not a criticism.
Frankly, I don't know of a perfect eccentric; they all have the subtle nuances and issues. If you can learn what they are and master them (or find a replacement to master if the issues with the original are insurmountable), you won't spend much time messing around with your eccentric. In which case it will only become an issue when you eventually go to loosen and service it, which is when they tend to act up.
The only "better mousetraps" that I've seen are the Bike Friday Family Tandem approach borrowed by Rob English for our
BF-brethern Ryan & Amy's Ti tandem down under and
a really artful approach by Dave Boehm on his very custom Bohemian tandem that took the People's Choice Award back at the 2007 NAHBS. Of course, better is relative. They were very unique approaches that demand a little more open-mindedness on the part of the owners and the Bohemian design probably wouldn't work with the newer BB / crank designs.
Me, I like the expanding clamshell design that Dennis Bushnell came up with and patented and have said so since taking delivery of our Erickson Signature tandem back in 1998. All but one of the tandems we've owned since then has used a Bushnell eccentric. However, and as previously noted, I've had to help friends rid creaks and squeaks from their Bushnell eccentrics when they neglected to find out how to adjust and maintain them and as much as I've mess around with the Bushnell's I've explored the limits of the torque specs and stripped a couple wedge bolts on our Calfee's Bushnell eccentrics.
Again, even the best ones aren't perfect unless they can remove "human-induced factors" from the equation.