I am flying with a portable unit and the range is 2-4nm and usually the 4nm in a direction I'm not looking.

I find the data useful for situational awareness, but far less useful for tactical decision making during a contest. Primarily because I typically have seen a circling glider well before they are visible on Flarm. If they were ten miles out, that would seem to be essentially useless information for me. That's 6-7 minutes at a pretty fast pace before I'm going to reach where they were. Assuming I saw them on flarm climbing at 10knots. Before I could reach them, they'd be topped out and gone and I'm left hoping that I can find that same thermal either recycling or miraculously still working..

Additionally, we are all leeches to some degree. If you spot a glider out in front of you or near your course line and they appear to be climbing well (or are confirmed by Flarm) I don't think any competitive pilot is going to avoid their thermal to be a sport and find their own lift. If they are a slower pilot you're going to probably leave them behind, a slightly faster pilot may end up marking lift for you. A much faster pilot will leave you behind.

My personal experience with Flarm in a contest is that I did not use it at all for competitor analysis. I always spotted a glider visually before getting an Alert to new traffic. If they were climbing and looked to be marking a good climb, I was heading that way based on visual cues, not Flarm cues.

I was team flying with a partner and kept it locked on him as long as he was closest. For that it was hugely valuable. When he was on my 5,6,7 position, I knew and it reduced the radio calls needed to alert each other to our position when tight and in a blind spot. For all of the other aspects of team flying, it was really a non factor as we used radio calls for more accurate info on lines and climb rate.

Non competition use I find that the buddy flying aspect is really only valuable for giving a higher degree of precision to what you can see with the eyeball. You're on glide with a friend, separated by 1/2 a mile. You know they are above or below you. You can see that change faster than inspect the Flarm. The Flarm just tells you that they are 150ft and now 160ft higher. It's interesting, but I just don't see it as more useful than what you get by looking outside.

Morgan