I've had the opportunity to test the top makes side by side for handling and optical comparison( although not able to compare all at dawn and dusk, but that depends on the individuals eyesight anyway so it doesn't really count).
These included swarovski E.Ls , leica ultravid , zeiss dialyt , zeiss night owls, kahles, meopta , nikon , and minox high grade. All were around the same magnification spec. ie 7 or 8 power and with 42ish objective.
To answer the question regarding the kahles; They are as good optically as the swarovskis( they should be as they use the same lenses) and the leicas, they come with the same warranty too.They are shorter in length too which is handier for tucking into your jacket before that last 50 yard crawl. Also bear in mind that they are around 400 quid cheaper.
The other ones worth thinking about are the minox HG series. These are easily on par with the swarovskis on optical quality and are about the same weight, they are are shorter so again easier to slip into your coat, carry the same warranty, AND are over 400 quid cheaper.
If weight is not an issue then i can seriously recommend the zeiss night owls, i have had the opportunity to compare these at low light with leicas and swarovskis and believe me...night owls won hands down. They were the 7x45 version.
Just think.. that 400 quid can get you a rangefinder and still have change to spend on the missus
