I just read a review of a wireless router extender (the Netgear N300, which I own and enjoy). The owner said that the extender worked fine with his previous Internet service provider, but with the new provider, he couldn't get it to work after "five or six hours" of trying. So he posted a negative review of the extender on Amazon.
Do you see the problem here? The rule is, If you change a variable in a working system, and the system stops working, look first at the variable you changed. Why blame another component in the system? That component worked fine before the change.
In the instance at hand, changing cable companies likely means a change in wireless routers. Maybe the new router (1) doesn't do WiFi well, (2) has the WiFi feature turned off, (3) isn't synchronized with the extender (unplugging the router for a minute has been known to work wonders). Or, perhaps the user is being impatient. A minute or two can be needed for the N300 to handshake with the router initially.
There is a tendency to blame the final link in any operational chain rather than investigate the upstream links. Here, the wireless extender is the final link and gets the blame. Come to think of it, the TV or laptop or BluRay player is probably the final link, so perhaps they should be investigated too.