I have tried several of the cheap ebay ones and all but one had issues. Mostly they focus beyond infinity but I have also had problems with screws falling out and loose/tight fit. I also have several Fotodiox adaptors and they are great. They fit properly and focus correctly and so far no screws have come out. I also have one from Metabones and it is top notch, although it was a bit more expensive.
I have gotten 4 adapters from Rainbow Imaging (they sell on eBay and I believe Amazon) and all of them have worked perfectly. I honestly see no reason to speed the cash on the more expensive ones. Plus, if you have a lot of old lenses it is super cheap to get one for each lens. Makes swapping lenses a lot easier, especially if you are using 3 different legacy mount and native lenses.