I dont know these pilots but I am part of their community. I am very sorry for their loss.
My remarks that follow have potentially nothing to do with this accident but I cant help but comment on see and avoid.
I fly with TCAS for much of the time. Recently, and for the first time, I used TCAS to find and then formate with another aircraft (not the usual way I go about this). If you get the chance try it. It is a very good way of demonstrating even when you know where the traffic is just how difficult it can be to spot, particularly when you are moving parallel and at a similar speed to the traffic.
I have had three close misses. On one occasion over Germany I wasn’t the handling pilot and was looking at some papers. A brief look up and another aircraft was coming straight towards us. I could not believe the other pilot had not see it, or it us for that matter. Very rapid intervention on my part avoided and almost certain mid air. The handling pilot to this day can not believe how it was possible he hadn’t seen the traffic.
On final it is very likely a pilot will become fixated on the threshold or will momentarily avert his gaze to operate the gear, or flaps, or some element concerned with configuring the aircraft for the landing.
There is a mountain of evidence to suggest that see and avoid is not reliable even at GA speeds. See and avoid is not the salvation of avoiding collisions most of the time.
In a few thousand of hours of flying in VMC I become more and more concerned to use everything I know and every aid I have to minimise my reliance on see and avoid. Having done so I try to be meticulous about maintaining my scan as the arbiter of last resort.
As another example of course our scan should have started in the climb out. Anywhere in the circuit and the risk of a collision is high. The fact is the vast majority of low time pilots will not see an aircraft that cuts through their climb out from a position above them and to the left or right.
The fact is in my opinion see and avoid does not work. It does not work because we are fallible. Fly with most pilots and watch what they are doing after the take off. Are they doing anything to look above the aircraft? Are they scanning left and right? Nah. They are fixated on what’s ahead, and tasks in the cockpit.
Fortunately collisions are very rare but don’t kid yourself that this is because we are all really good at seeing and avoiding each other. Fact is the "perfect" pilot might do a reasonable job relying on see and avoid most of the time but there are very few among us that are perfect pilots.
In my opinion you are deluding yourself if you believe see and avoid will always ensure you avoid other traffic - I think we all dance on that particular pin head, and stay on the head but for the Grace of God - sadly in this case whether for this reason or some other reason these pilots luck ran out.
If you can guarantee me you would have avoided this collision or any other 100% of the time you have a great deal more courage in your convictions than I would or you have caught a healthy dose of blind faith.
IMHO if you take nothing from this thread other than more than a few pilots telling you that in their opinion see and avoid is not reliable which in turn leads you to question your approach to VFR flying outside CAS something will have been achieved.