I have not found either heat dissipation or lack of friction to be an issue at all with stainless tube bars. To date I have had no control issues with SS bars, yes they are faster than ally but, providing you are aware of this, it is not an issue.
Controlling a descent on a micro rack is quite a subtle process. Unlike a Stop this is a variable friction device, you can control friction either by altering the spacing of the bars (bringing them closer together increases friction, separating them reduces friction) or by running on four bars or five (adding in the hyper bar). Both these can be altered without any problems whilst descending. On a short pitch without much rope below me I may run on five bars with the bars closer together. On a longer pitch I may run on four spread bars, if I feel that I need more friction lower down the pitch I can either push the bars closer together or take the rope around the hyper bar so I am now running on five bars. Speed of descent is also controlled by the amount of rope running through the device (in much the same way as a Stop). I always start a descent on five closely spaced bars for maximum friction until I get the feel of the rope, I will then alter the set up on the rack to suit conditions.
With regard to wear and razor blade edges: Unlike ally bars wear on SS is very slow. I used schedule 40 tube which is thick walled (2.77mm); that will take a lot of wear before nastiness happens. You are simply not going to put (say) a three mil groove into a SS bar on any trip. As yet I have no wear on my bars in spite of a number of trips on mucky rope which would have eaten ally bars. If and when wear starts to develop I will bin the bars well before they get to a critical stage. Like all vertical kit you need to constantly monitor condition and chuck it before it becomes a liability.
SS rack bars are the way to go.