Pretty much a repeater should only be used when your choice is having no signal compared to a crappy repeated signal. You have to look at a repeater as it is better than not have wireless at all. Any wireless repeater will greatly degrade the signal quality.
I do not like these type of units that plug into the wall outlets. A repeater needs to be located in area that it gets a strong signal from the main router but can still provide a good signal to the remote location. Wall outlets are many times behind furniture or other inconvenient places. Stand alone devices you could place on a table tend to get better coverage because they are away from things blocking the signal.
You will not find a huge difference in these units...