Belloni's method has been discussed here in other threads. The Formate method was quite impractical IIRC. The alternative approach by Munter et. al. at Kodak using Osmate salts was most effective. I believe that Belloni's method was studied at Kodak by Eikenberry as noted in another post. It was found to be quite unstable. Even the Osmate approach renders film less stable and more prone to change during keeping and in my understanding, this is the major design problem faced in the 2 electron sensitization methods.
I believe that Belloni or one of the other workers on the formate method has tried to sue Kodak over the 2 electron sensitization, at least I heard something to that effect. Also, Belloni or some of the workers sold the rights of this method to Agfa just before they went under several years back.
The osmate system is indeed a surface effect, but a very effective one at that surface which yields about one stop in speed from a given emulsion. So, today's 100 speed emulsion, with all that can be done, is actually more like a 12.5 or 25 speed emulsion from years back when one considers Sulfur+Gold, Supersensitizers and 2 Electron Sensitization. This improvement also includes Iridium and/or Rhodium doping for Latent Image Keeping and Reciprocity Failure fixes. So, in spite of all of the "complaints" here, today's films are better for speed, sharpness and grain and actually have better keeping than those of about 25 - 50 years ago.