Good so far, and support has been encouraging
The battery in my five-year-old Macbook Air was faltering, so I read the reviews and ordered an ifixit replacement.
The repair was easier than I could have imagined, the only trick being handling the tiny screws, but the magnetic screwdrivers took care of that. After that, the battery started strong but has been losing capacity a little each day (my Coconut Battery app tracks it), but ifixit tells me battery charge with fluctuate the first 30 days before settling, and promised to replace it if it doesn't, so I'm willing to see how it goes. Customer service has been fast and helpful, and I have the impression that this is a company that stands by its products.
After you've unscrewed everything and carefully laid your screws where you can access them to replace them, and then you remove the bottom laptop plate and see how dusty the inside of the laptop is, don't blow into the plate to remove the dust if the screws are behind the plate in the same path where you're blowing. Those little suckers go flying!
Beyond that, based on my experience, if anyone else's is like mine, I'd say give these folks the benefit of the doubt and give the battery time to settle in. Support has been fast and responsive.