I installed these yesterday. From the first moment I could tell they were going to be perfect in my system.
My system is bi-amped - a Pioneer SA9500II for woofers, Cambridge Azur 840A (mk 1) for tweeters. Added to this is a Temblor T10 subwoofer, dbx 234xs active crossover, Tannoy System 800 monitors. Not audiophile kit, but it all serves my musical muscle memory very well.
The tweeters on the System 800 have never done it for me. The System 800 was designed to reveal flaws in mixes, which it does very well. However as most of the music I listen to has flaws, it can ruin enjoyment. I have retained the woofers from the System 800 (Tannoy 2046) as I really like the mids and low end these speakers provide.
The reason I chose the Atohm tweeters was because they have an extended top end well beyond 20 Khz, and that they are fairly flat up to 20Khz. I wanted to cross them over fairly high as I want to use the Tannoy 2046 drivers over their full useable frequency range - 70 hz to about 3.5K. I've got the cross over set at about 4 k and it sounds great.
The frequency response of these tweeters is superb - no harshness, smooth, sweet and airy. Build quality is excellent. Off axis response is so good that you can walk around and not miss anything.
I think they'd sound great crossed over any where between 2k and 5k - very flexible. They may even cut it as super tweeters.
Mine are mounted on open baffles sitting on top of the System 800's, each protected by a 30uF capacitor. No phase problems at all, which surprised me. Highly recommend.
Note : don't build your baffles until you see the reverse of the tweeter (like I did) ! The digaram is slightly confusing regarding the hole you'll need. It's actually 72mm with notches cut out for the connection tags, not 84mm in the round.