4th back surg coming is revision decompression and there is narrowing of the nerv canal. what advantage is over pain stimulator?

Depends on your : Symptoms & whether they match your imaging findings. A decompression works well for leg symptoms brought on by standing & walking relieved by sitting. Make sure you have no hip or vascular issues or a neuropathy. The success of repeat surgery generally decreases with each one. A stimulator is reversible & does not preclude further surgery.