I've not used them but know people who have and the weight goes straight back on.
The problem is rarely do people use weightloss injections as part of a life overhaul. People aren't increasing exercise or implementing a healthy diet so as soon as the injections are stopped they go back to the same lifestyle that led them to gain weight in the first place.
Long term weightloss only happens with a commitment to changing lifestyle. Injections are a quick fix and without actual dietary change or exercise the weight will always go back on.