Also owner of a Roborock S50, can confirm, bang for the buck is much better than with Roombas. My only gripe is indeed that the maps are not persistent. In fact it's even more absurd, they are persistent in the sense that you can see previous maps, they are stored, but it doesn't take them into account to optimize the next cleaning session and, more importantly, you cannot use them for the ever useful zoned cleaning function. Why? It seems that all the components needed are already there, and looks like it should be a trivial software update to enable this.
Anyway, an amazing vacuum and absolutely great for the price.
I also recently bought one and noticed the same, but then I think I understood the reason for not persisting the maps, when the robot found a closed door: after I opened the door, the robot just wouldn't cross it because of the (temporarily) stored temporary obstacle.
Storing a map also means you need to have a very good way to update it.
Anyway, an amazing vacuum and absolutely great for the price.