The only problem with biax tape is only half of the fibers are working for you, the rest are parallel to the seam and do nothing.
Same problem with woven tape.
Tape cut on a bias has all the fibers working for you.

Sorry Bill. You're wrong on this one.

Biaxial braided tape is woven with alternating fiber angles, not flat like in the woven tape. All of teh fibers will cross the joint. You can vary the angle depending on how much the tape is expanded or contracted. If you pull the tape from the ends and contract it fully, the fibers will be running nearly parallel with the length. When expanded they cross at about a 45* angle. The carbon tape is shown below but they also make it in fiberglass. See below:

Compressed:

Expanded:

The ultimate joint reinforcement would be to buy some wide unidirectional cloth and cut narrow strips across the width. ALL the fibers would be crossing the joint. Something to look at for ultra-light construction maybe.

This talk is all pretty silly though. How many times have joints failed using regular, woven or bias-cut glass cloth?!