I have a few of them, they work pretty good. One thing I like, is you dont have to put a block under it like some do with the screened bottom board in the winter, the tubes block about 75% of the air flow and allow more stuff to fall past.
I believe they are out of buisness now, thats what I was told over a ruhl bee supply in portland.
I made some of my own with 1 inch grey pvc, cost about 4 bucks each. Ruhl has some in stock, they are about $ 39 each.. ouch
The almost clear tubes that the happy beekeeper used seemed to flex a but to much and allow bees to squeeze past. The Grey dosn't allow that to happen. The 5 hives I had on them last year did fine.