I presently use two levers quite often, one an M94 in .30-30, the second a Guide Gun in .45-70. I have both outfitted with Williams FP sights, but not the firesight front. I am afraid they (the firesight) would be too fragile, but the rear sight is very capable of taking rough handling.
There are two advantages, for me, to using the receiver sight. One is that I can see with it better (less target covered, suits my eyes, etc.), and the second is that on both rifles the increase in sight radius helped reduce the group size to where I am very confident of both rifles' accuracy if used within their capabilities.
I have experience with the Williams, but keep in mind there are other brands that you may like better, such as the Skinner. A good receiver sight is a worthy upgrade.
