I think it is great that Howard has stepped forward and tried the idea of boost tabs on a serious PA model. I am looking forward to get a model finished sometime next spring for me to see how much they help.
There was a model at the 2004 World Championships in Muncie that had the boost tabs on the flaps. I did not get to see the airplane fly and only had a short conversation with the flier. I do not even remember which country he was from (Australia??).
I think that there is little weight penalty to incorporate this concept for the flaps and/or elevators. They cannot hurt and might even help a bit.
There was an article published in Model Airplane News prior to 1994 titled "Labor-Saving Devices for Overworked Servos". The article has been republished in the MAN publication titled "How To's, Volume 2". The article discusses aerodynamic balances, paddle balancers, and boost tabs. It goes into quite a bit of detail about the boost tabs to show how they work, why they work, and how to size them. Though this was written for RC, the application works for CL.
There are several full size aircraft that use boost tabs to control the moving surfaces of the aircraft. Examples are the Douglas DC9. The B-29 used them to control the ailerons, elevators and rudder, all without hydraulics. Also, I think the Boeing 727 uses boost tabs.
By the way, there are a lot of good ideas published in those two "How To's" volumes by Model Airplane News.