JBiorn, my brother uses that method but it feels awkward as heck to me.
Whether using the stringer, push-pull step thru or knee in the handle you are never over stressing a limb as it will never be bent much more than brace height, and certainly no where near full draw. There is as someone else stated a chance of twisting wide thin limbs on a curve whether using a stringer or not (I've seen the string slip over the edge of a limb just prior to pulling up on the riser of a recurve), This could certainly induce twist, however on a recurve I would still recommend using a stringer carefully. I have also seen a limb tip fly out of a shallow pocket on a stringer.
There is no absolutely safe method, but a little inherant risk in all methods. I have been around stick bows my whole life. Been around tens of thousands of guys stringing and unstringing trad bows. I have never seen anyone come close to getting an eye poked out, nor do I know anybody who has known of someone actually doing this that I could verify. It may have happened to someone sometime, but personally I think that's more of an urban myth. I did see a guy knock himself out once trying to draw a 125# recurve and the bow slipped out of his hand and came back and smacked him on the forehead right between his eyes.
Heck I ride motorcycles, big fast ones. I know inherent risk and I'll take my chances stringing a straight end bow with the push pull method. I even take my chances and wear a full face helmet even though "supposedly" a full face helmet caused someone to snap their neck in a wreck once.