...recommend the I-beam as being the only one that works reliably without feedback, bark, quack, hum or distortion and yet is very easy to install and needs no holes drilled at all

The I-beam is certainly very good but the PUTW that I referenced above is certainly in the same league, if not superior, with similar features. I have tried both and mention the PUTW as it is less well-known (it is a small company)

Zen