Both are good scopes.
To me, March FX has a very slight edge in clarity. Also, the 4.5-28Ă—52WA is something to behold for FOV. 4.5x seems as wide of a FOV and my K318i set on 3x.
The other thing that really takes som getting used to is the top parallax ring. I am so accustomed to a left parallax, I find it difficult to grab the forst time using it when switching back and forth.
I think both turrets are about the same tactile feel and sound, a touch muted compared to some other top end scopes.
The K525i has much better glass than the first Gen K624i.
The availability of a right side windage on the Kahles is nice if you want that. I don't, so it doesn't matter.
Kahles are easier to find. And, it is the oldest scope manufacturer still in existence.
March is lighter weight.
Both are bright enough for any legal hunting you might do.
Both are much better than a NF NX8, maybe slightly better than NF ATACR glass.
I would give the robustness edge to Kahles, even though I am pretty careful with my scopes. I also haven't heard any I can recall of either going down.
I like the Kahles reticles better, but either work great.
I think Kahles illumination is a bit brighter on max.
The March High Master glass is far better than their standard "ED" glass. Doesn't even compare.
Honestly, I would buy whichever you can find used. I don't think I would buy either for the "new" asking price of $3200+. But both can usually be found used at decent prices.