Cisco (Avid Vapor) warns about using their 1.5, 1.8 and 2.0 atties on egos, rivas and the like, but that warning may be a bit out of date (I dunno).
My experience with cisco 306 atties (mainly 1.8 ohm), on my egos, is what may have caused problems with ciscos and the egos in the past, is the fact that the ciscos, tend to drop in resistance at times.
Now, Joye... sells 1.5 ohm atties for the ego (both 510 and 306) so... you would think that down to 1.5 ohms might be fine for egos. But, I have seen cisco 1.8 ohm atties drop almost down to 1.5 ohms... and I saw a review of the cisco 1.5 ohm atty on utube and, the guy said it metered in at 1.3 ohms. So, you get that low in resistance and, you may indeed damage your egos.
Also, I am not sure about this but, my guess is the newer egos, the ones with Joyeteck or Ego-T on them, have better protection circuitry.
In any case, I have been using the 1.8 ohm ciscos on my egos for maybe 8 months, these are the only atomizers I use (306, 1.8 ohm and, I pick out the wicks), and so far no problems with my egos. I have been thinking that maybe I am being TOO conservative and should go for the 1.5 ohmers ... where I can get bridgeless... but, maybe not hard to say.
But, they do have that warning there so you will have to decide if it is worth the risk or not.
Yeah, they don't say don't use them on egos, rivas and the like, they say 'use at your own risk'.
Hope this helps.
Z