I speak as contractor based in Dublin.
There is a lot of truth in this post by those on both sides of the argument. On the whole you never do feel part of the EI family, you seem to find yourself as an outsider. The airline is run by those whom joined at 18 under cadet schemes. There is a lot of bickering inside Aer Lingus about siniority especially those approaching the magic left seat and those in the left outside Dublin (Heathrow/Gatwick/Belfast) waiting to get in.
They keep you loyal with the promise of extensions and the chance of being made permanent. You may well get an extension if your contract runs out at a time when FOs are needed. As far as being made permanent: You have as much chance of that if you were applying as an outsider for the Direct Entry scheme as contractors must also apply this way and conduct the screening as if they have never set foot on a green plane.
All in all, if I can give you my sincerest advise, if you want a quick stop in Europe to fly the A320 by all means this may be for you. However do not bank your career on this, you will have no seniority for the entire length of your service and those cadets joining every year whom do not even have a PPL are automatically above you. If you do make it as a permanent FO which I would say is a %20 chance, you will start at the bottom needing at least 12 years for the left seat and maybe 18-20 for left seat A330.
This is what I have seen first hand, take it or leave it. It is an extremely good experience, if like myself you use it as a stepping stone for other carriers.