We rented a boat twice: first at Sfakia, then at Marathi location of the same company.
Overall experience was very positive, especially at Marathi, and hence the rating I put is the highest. You will receive an App on your phone with the map and borders for your travelling range, and all instructions before departure. The range is large enough and places to stop are numerous, easily covering one full day.
Some critics too: the man instructing and then fueling at the Sfakia locations needs to learn a bit of being more customer friendly. Specifically, we had a small problem - our anchor got stucj betweek rocks and could not get it off the bottom for quite a while. I called, as instructed, the man at the base. He gave some instructions over the phone, and naturally, there is a bit of language barrier, so one must exercise the mutual patience. Of his instructions, 50% of the time was literally: "You loose the Anchor - you'll pay a lot", in a rather unfriendly voice. You clearly do not hel people this way. Think about that, as such experiences spoil the whole impression.
Now, about the Marathi location - the guy was utmost professional and friendly. For isntance, he upfront instructed that should you you have a stuck anchor, you fix a boije to the same rope on the other side, and leave it so, if unable to unstuck your anchor.