Actually I used both in cadets for long distance shooting, it was always easier to use the circles as the post obscures what you are aiming at, however we were shooting at between 100 and 600m. It was also easier getting the foresight lined up exactly as you could make the gap around the edge the same between the two. Personal preference though.
The circle ones are Parker Hill sights, and it's way easier carrying out aiming off drills with them as you can actually see the sand splash, unlike with post sights. I've shot 7.62 at 300, 500 and 1000m with that kind of sight, and I've also shot .22 at 25, 50 and 100m with them.
We use the standard sights on the L98A2 GP rifle though.
I think shooting's better in cadets- you don't have to pay for the ammunition. I went through almost a grand's worth of 5.56 on the weekend and I only paid £5 for catering and transport. Thank you, MoD
a grand's worth of 5.56? I doubt it, unless you went through about 16,000 bullets in a weekend! Who knows, maybe they're letting cadets play with miniguns now?