Ive had a response from a very helpful ebay seller re dongles:
'yes it will work in Turkey as long as the network you are going to use is working on 2100MHz (what is most likely as it's standard for Europe) Turkcell certainly is.'
So, my next question, is can I go into a Turkcell or Vodafone shop and just get a mobile internet sim on payg without buying their dongle?
Kevin B said its 29tl for a 4gb a month, not sure who this is with, do they all charge about the same?
And do I just need my passport to buy it?