After years of lacking a quality striker, all of sudden the Ethniki has 3 playing at a high level + Tzimas about to join a Premier League side. And you can throw in Kostoulas to that mix, although I am not sure that he actually has a natural position and I don't think he is an out and out striker.
As a general rule, I don't think Greek footballers should be moving at such a young age to England. It didn't work out for Tzolis, Tsimikas really had to bide his time and was almost unsighted for a whole season until becoming a trusted depth player. Mavropanos went to Arsenal super young and eventually had to move to Germany for 2-3 years before moving back to EPL. I just don't think it suits our young players, especially so early in their professional careers.
Different to go back as a more seasoned professional who has spent a few years playing abroad. Which is why I think moving to Germany should always be the priority. Beyond that, Portugal, Belgium and even Holland are a good smaller step-up before making a bigger leap. These countries and leagues have a reputation for developing talent and being patient. Unlike your England's, Spain's and Italy's which are a lot more cut throat.
I hope Tzimas is the exception, Brighton has become known for signing talents and on selling them for a big profit. There is always added pressure and expectation when you come with a decently sized price tag. Good luck to the kid and I am sure he will get his shot with the Ethniki in the near-ish future.