I can't say that I have full insight in what is happening but I'll try to share what I know.
From the 10 towers FerroNats got, several have been already transfered. This is a huge delay to the initial planning where it was supposed that all 10 would have been transferred prior to previous summer.
The professional level of the new atcos has been significantly lower that the previous trainees (you thought it couldn't get worse in Spain? We have a saying here: others will come after me that will make me look good) which in combination with several legal and/or organization mishaps are root causes for these delays.
The two most important airports in the pack in terms of traffic (LEVC and LEAL) have not been transfered yet although the schedule is to have that before summer. Considering the accuracy of these predictions so far I'd take that estimate with a grain of salt.
In any case it seems that FerroNats has not enough staff as they have been forced to keep some trainees failed in training at a specific tower and they have just moved them to a different one to start training there agian. Unlikely scenario if they had surplus of them...
The contract was awarded for 5 years with a possible extension of one more. Obviously this being a country with the same political integrity as Greece or Italy, all bets are off on what might happen.
One of the few solid facts are the economic and working conditions offered by FerroNats... they have been posted before both in this thread and on other ones about spanish ATC but if you need them, feel free to ask.
Bottom line: You can probably get a job at FerroNats but I would advise to check carefully what you are getting into. Feel free to ask, I work for Aena but I can provide link to official sources so you can make your own opinion.