This is my Harrisville rug loom. I don't know anyone else who weaves tapestry on one, but I would like to recommend it as a fantastic tapestry loom.
When the warp threads are wrapped around and around a back beam, they fall in between each other and the tension in my experience is never even when you start advancing. Even if you are one of the million-stick-club and you are very meticulous about winding your warp with sticks, things can go awry easily. The warp extender pulls all the threads up evenly around a smooth steel tube. You start your tapestry with the extender raised, tie on and get everything even, and then as you weave and pull the piece forward, instead of unwinding the warp beam, you lower the extender. Genius.
And of course it is a countermarche loom and I love the fact that the warp threads get pulled evenly from either direction on each shed. I like things even. Perhaps it is a good thing for tapestry or perhaps I just have a touch of OCD.
This picture is looking from the front of the loom toward the back with the warp extender raised.