The flimsy spars of the dimestore kite will snap easily if overstressed. Thus it is relatively safe to fly such a kite. A kite made of ripstop nylon, carbon filament spars and flown with heavy duty nylon cord is a very different item that must be respected. Rope burns can happen quickly and cut to the bone or worse. Hand protection is mandatory.
Rope burns are terrible.
It is well worthwhile to invest in a small parafoil or winged box kite suitable for 40 or 50 pound line and test fly it to get a feel for heavy duty kites. Remember, a kite twice as large is going to have a pull four times as great or more. The large military kites were flown from special trucks that carried large drum wenches. The jeep would go around an oval course while 50 caliber machine gun trainees would blast away at the kite above. A friend had one of these and we would fly it in Oklahoma from the ground using a 4x4 as a flight handle.