I used work with the RM manager who was responsible for foreign postings of both parcels and mail.
Basically what you need to keep in the back of your head is that ELTA is the company that will take your money in exchange for delivering your item.
Nearly all international couriers take the item off you using their own system and will take it to a port where it goes into either an aircraft or a ship along with all the other couriers stuff. ELTA have subbed the entire shipping operation along with subbing the final delivery operation once it hits the UK. Fred Bloggs and co will finally deliver it to your door.
Therefore the chances are that your item is in the same container as all of ELTA's competitors, so the service and tracking are virtually identical.
As sweeping statement I would guess that ELTA change the shipper and final courier every 12 months as it is a very competitive game, so some ones experience of 12 months ago is not a direct comparison with what happens today.
What I can say from memory is that the carriage of items in Greece is generally good with minimal loss, theft or mis delivery, but things can hang around overnight. Deliveries, however, out of Greece to the port are good as it is nearly always on time.
The cross continental service is identical with all couriers because they are on the same ship / aircraft.
The main worry from your POV is who are they using to make the final delivery to your front door.
From former colleagues in the business, despite horror stories of stuff being left in greenhouses etc, the level of successful and ontime international deliveries is pretty good. This is mainly due to pressure on the industry from the likes of RM, Parcelforce, Amazon and ebay.
If I was in your shoes, the main question I would be asking ELTA is a breakdown of the tracking procedure and at what stages is the progress published.
If you are happy with the level and frequency of progress detail from ELTA, then go for it.