I think the poster is simply naive.
There is a misconception that the radio and transponder in some way prevents collisions in open FIR. That misconception can only arise from failing to understand how they work.
As others have said a transponder is of no use at all in collision avoidance (unless you have TCAS fitted, which is hardly anyone), or are receiving a RIS or RAS (which is most unlikely in open FIR).
Radio calls informing everyone of your position and height may be of some small help, in that other alert pilots may realise there is a potential conflict or adjust their height to ensure one does not arise. The problem is that on busy days when collisions are more likely it is often difficult or impossible to make frequent position reports. Moreover, pilots are likely to be talking to different stations - are they with London or working a local ATZ. They are also unlikely to know the local area well enough to know when a pilot calls overhead XXX that they are in the same area.
As I posted on another thread there are a number of ways in IMC you can reduce the risk of collision in open FIR. These ways apply equally in VMC with some additions.
1. Avoid overflying choke points - VORs, NDBs and VRPs
2. Avoid tracking close to the edge of CZ
3. Fly above 3,000 feet if possible, most GA pilots don’t like getting to high
4. Avoid gliding sites and any airfields
5. Avoid following line features - I suspect most GA pilots have forgotten the rules about line features and simply follow them regardless of which side they should be on
6. Fly at 2,000 feet (if you cant get high). Slightly tongue in cheek but everyone is told don’t fly at 2,000 feet and seem to have got to grips with that one, so now everyone is at some other height and 2,000 feet is presumably pretty conflict free
7. Never fly in a straight line, make small and frequent course changes