It doesn't always work out that way, Danny/Filippos. This time it took me 80 minutes at Souda IKA. I have also been when it only took me 30 minutes. Equally there have been times when it took me almost 3 hours. I have only done it once at KEP and it took about ten minutes. On the downside I did have to visit twice but to me that is better than sitting around waiting.
I have used KEP to transfer ownership of two vehicles, one selling and one buying, and I have also exchanged one directly at the vehicle centre, buying in that case. KEP was easier and they also sorted out a major problem where one vehicle apparently had a lien on the ownership. I am absolutely certain I would not have been able to resolve that problem myself.
I originally transferred from a UK driving licence to a Greek licence myself at a driving centre. Since, I have renewed it twice using KEP. Again the process using KEP was much simpler.
I am completely flexible but I do like an easy life and often KEP makes life much easier.
Typically when using a KEP enabled procedure you are going to leave some document with KEP and then get it back at some time in the future. KEP take a photocopy of your passport and keep it with their file. When you go to collect the document they can use your passport to check your identity against that logged when the procedure was initiated even if it is a completely different person who deals with it. Even if you are just signing a document in front of KEP they need to check your identity so needing to present a passport is not unusual. Since you are supposed to carry your passport at all times I don't see this as a problem.
I was asked by KEP for my Residence Certificate when registering change of ownership of a vehicle and when renewing my driving licence but since these procedures are supposed to require a Residence Certificate anyway that again is not surprising. I was not asked for it the one time I renewed my IKA book at KEP. Since you need an IKA book to get a Residence Certificate, unless you have some other form of health insurance, it seems a little odd if you need a Residence Certificate to renew an IKA book?