I dunno, but for surfing the web and watching YouTube, I'd never turn to a black-and-white e-reader. Especially at that price of many hundreds of dollars!
My solution is to use regular tablets for those two activities, which can be a lot cheaper, but still of solid quality.
At the same time, I admit I'm happy my newest Onyx e-reader runs on Android, so that I can perform "tablet-like" activities on it, if need be. But I really only consider it an
emergency option.
For around $500, I'd consider the newly released 10-inch
Onyx Boox Air2 Plus. (Not just Air2 – Air2
Plus, which has a larger battery.) But it really seems like a stretch.
(I have the cheapest, 6-inch $150 Onyx e-reader, and I'm perfectly satisfied with it, but I'd never turn to it for specifically performing the activities you listed.)