The feed necks are very similar, but they aren't the same.
The Etek and Etek2 - along with those of the '05 and '06 Egos - had an o-ring around the feed stub. The lower collar of the feed neck clamped on to this o-ring. From the Ego7 onwards, you just had a plain feed stub with no o-ring. The feed neck clamped directly on to the feed stub. This change lead to a change in the dimensions of the stub and the neck.
Consequently, an Etek feed neck may not secure to a Geo feed stub correctly.
Although an Ego 7-10/Etek3 Feednecks will physically fit over and onto the feedneck stub of a Geo, you will notice that they are slightly lower at the back than the front, so will not sit flat onto the Geo's body.
I did spot that the bottom of the Ego feed neck was angled, where the Geo feed neck was flat, but the Ego feed neck still seemed to fit OK (I actually did the swap before answering I never trust myself to answer from memory!)