I have dabbled a little around Plakias, using rental bikes, but frankly they are not up to serious usage, although they are reputable brands....cube, giant ect. As they say in Ireland,if you want to go somewhere, don't start from here. I have little doubt that you make some decent routes, but there are better places in hi Crete to start from. Maybe kousteyeriako or sougia or even paleohora. Also if you ride anything away from the ordinary, spares are difficult, I remember talking to a guy looking for 29er tyres, no way in Greece. I would be interested in hearing how you get on if you try.