have for a while now and love it! it's now installed on my 10 gallons mt kettle and will be move to my 20 gallons this week-end! I never used it with gravity tho, it's hookep up to a pump!
I have used one for about a year now. Dead nuts simple and effective. So much easier than fly sparging. Also, it works well for pump circulation during the mash. Very nice product. Well worth the price.
My HLT gravity drains into my MLT so I have never felt the need for an automated device, the flow rate into the MLT just isn't that critical as long as the grain bed stays covered.