Is it accurate enough for primary instrument for speed ?
I used the Hall wind meter for a couple of seasons on XL-58. As to whether or not it is "accurate enough" depends on your expectations. It was the only airspeed instrument on my Eagle and I found it adequate for general use. If you need something to nail down precise power settings and landing speeds then it probably won't have enough resolution. It is also sensitive to angle of attack at low (landing) speeds.
But a proficient pilot doesn't need an airspeed indicator on a Legal Eagle for safe flight. Learn the characteristics of the plane and you will rarely check the instrument.
Having said that, I now have a conventional airspeed indicator on XL-58 and find it useful primarily as a VSI since I don't have an altimeter. If airspeed is decaying, we must be climbing...if it is increasing, the ground must be getting closer.
A very useful flight instrument for learning the Eagle is a lift reserve (angle of attack) indicator:
http://eaglexl-58.com/lri.htm
It is far more accurate than an airspeed indicator for analyzing stall characteristics. While I had it on the plane it was the primary instrument instead of the Hall meter.
