We have two and have discussed this and decided more than two would be confusing. They have only one function: the All-Upper telling the ride leader of any problems. The ride leaders need the walkie-talkie as they make decisions based on info from the back.
The only time we'd change that would be, for instance, when leading 21 people through the centre of Amsterdam in rush hour (
@Gordon P knows how stressful that can be), when the ride leader would hand the walkie talkie to someone else and concentrate on navigation. The carrier of the walkie talkie then does ride management (allocating waymarkers, regrouping, etc).
We're getting there: no one else does what we do in such numbers and such circumstances (darkness, bad weather, foreign lands, large numbers etc) so there's no one to learn from. But we're just about on the ball now.)