Yes, I use them on our H3's and TiVo Roamios (basic). The Roamio (basic) is notorious for having a very poor fan and airflow.
I would say that in my experience the key is airflow from the BOTTOM. In the past just placing casters under each of the four feet of a Dish DVR box lifting it some 1/2" or so can do WONDERS without a laptop fan. However, if casters are not enough to take the heat off, then laptop fans are an economical solution: they work even better WONDERS.
Glad you got the solution. And be aware that even a few degrees of heat in a room during the summer can make a DVR like the Hopper or TiVo Roamio (basic) get very HOT.
