The right answer is to fly as the flight manual states. I expect that it specifies a flaps up glide. When your glide transitions from a glide for distance to the approach for landing, obviously some, hopefully all flaps will be extended.
Early extension of flaps will increase lift, which you do not need ("cause you got no thrust"), and will increase drag, which you really don't want then. Consider that increased drag will increase your descent angle. That might be what you want, but be careful what you ask for, you might get it. Remember that chances of survival are inversely proportional to angle of arrival. When you develop that steep descent angle, you'll want to convert it into a very shallow one before landing. This requires energy, which you do not have from the engine, so its you inertia only. With a lot of drag that goes away fast.
When I do familiarizing flying with owners in their STOL modified aircraft I would demonstrate, and train not to glide at speeds slower, or with more drag, than the flight manual states. You can do it, but slower means less inertia, and when you go to flare, there;s nothing left, and you stall and drop in unable to arrest your rate of descent.
You'll find many cases where flight can be accomplished at slower speeds or different configurations than the flight manual states. The plane might do it, but you may have unwittingly given up a reserve of safety (inertia) which did not even think about.
Yes, safely learn and understand, but ultimately you'll find the flight manual way is the best way - I've done a lot of flight testing, and that's what I have found....