I got their 6E mesh router a while back from Costco after my dismissal experience with Netgear's Nighthawk mesh router. The signal strength was excellent, the units were interchangeable, and the app worked without delays. All of that, and it was around $200. I'm not surprised they're popular.
Edit: I think I read "modem" instead of router in the title when I originally wrote this. Edited for a slight bit of clarity.
When they are cheap as chips and you can sell them for regular price it makes sense they have good coverage in the market. I remember the ones we sold had RJ45 with only 4 out of the 8 pins installed.
We use to buy them for $20 wholesale and sell them for ~$60.