So I actually did buy DD-WRT pre-installed on a refurbished router from a company called FlashRouters. My experience was pretty good, the router lasted ~4 years until the hardware failed. I decided not to buy my next router from the same company afterwards, for two reasons

1. they automatically enrolled me in a 'support' subscription I didn't want and I didn't realize until it renewed once, then I cancelled. it's apparently not easy selling flashed routers.

I don't begrudge them for this, though: I'm guessing they actually do have a lot of users contact support, and this business practice was a rock and a hard place situation: you don't want users to fail to install the device nor to have a bad experience because you can't afford a skilled support team. I'm not sure if they have since changed their policies.

2. I learned that, all along, ASUS has built their routers on a company-maintained downstream flavor of WRT.

So I just bought an ASUS router and haven't looked back. When I first set it up I was able to go into the admin ui and configure it similarly to how I had configured DD-WRT.