Back blows are the proper first-aid measure for dislodging an object that blocks the airway.
The problem with the Heimlich manoeuvre isn't so much that it's ineffective but that in order for it to be effective you have to exert an enormous amount of pressure on the abdomen, which in turn can cause severe injuries. That potential trade-off might still be worth it if the person otherwise would choke to death and there's no other help available but it makes it something of a measure of last resort.
The problem with the Heimlich manoeuvre isn't so much that it's ineffective but that in order for it to be effective you have to exert an enormous amount of pressure on the abdomen, which in turn can cause severe injuries. That potential trade-off might still be worth it if the person otherwise would choke to death and there's no other help available but it makes it something of a measure of last resort.