I've tried the Telex 850 and also the Bose A20.
The Telex is light, takes up almost no room in a flight bag and the mix seems good quality.
However I personally found it a bit uncomfortable (Most people say the opposite) due to the on ear design, I don't get on overly well with on ear designs. I had to remove them for a minute or two during cruise to give my ears a rest. It also may have been a problem with my headset but the side tone was not noticeable unless the volume on the audio panel was turned up to uncomfortable levels. I found it distracting not to hear side tone and kept having to check the mic was working (it always was to be fair).
The Bose A20 is what I prefer to use. It takes up much more space in the bag, it is heavier and it also needs batteries which the 850 doesn't, however the noise canceling is leaps and bounds ahead of just about anything else (aside from maybe light speeds which come close) and even though it is heavier and 'clamps' more, I don't find it uncomfortable after wearing it for the whole day.