I have the 18x by Sig. For 10x and below image stabilization is not needed - above 10 physical (tripod) or electronic is a necessity. I use them for hunting whitetails from a blind. The typical target area on my place is around 250 yards. With stabilized optics at 18 power, I can very quickly age a deer at that range and know exactly what I am shooting. For instance, year before last I took a spindly eight pointer that with normal optics I would have judged a 4 1/2 and never shot. With the stabilized 18x he was clearly actually very old - teeth indicated 6 1/2 - 7 1/2.
However, I would not take them on most of my normal hunting in the Americas or Africa. There 10x seems about ideal and the range finding capability of my Leica's is essential. I am debating whether to take them to Europe this spring for judging roe deer.