Many people curse their wi-fi extenders because they site them in the wrong position. For example, if your router is at the front of your house and you're getting a lousy wi-fi signal at the back of your house, putting a wi-fi extender at the back of the house won't help. It need to be in the middle of the house, where it can receive a good signal and then pass it on from there.
With that said, most wi-fi extenders are reasonably good at their jobs, although the construction of some buildings can cause problems.
PC Mag is an excellent source of independent reviews:
https://uk.pcmag.com/wireless-networking/89243/the-best-wireless-range-extenders
(NB: Make sure that you click the 'right' arrow, near to the top of the page, to see all 12 products, rather than just the 5 that you initially see. Each one of those 12 is rated 'best' under different circumstances).