I believe
@samnaz (You can check out her build thread from her profile) has one, there are a few users here who do. The issue with finding a ton of reviews on them is that most people looking for smaller nano tanks, prefer the AIO setup. Also a lot of people looking at these sized tanks are usually talked into slightly larger ones. Although I will admit, going with a sump on my nano was the best decision I ever made and I'd never suggest not doing it.
These tanks have only been on the market for just over a year now as well so still young. Personally I really love these tanks as they provide SO much more than the usual nanos do. IM tanks are fantastic and you won't be disappointed, keep in mind you will need a stand and sump as well as some basic plumbing as the tanks don't come with everything. Other than that, they are beautiful tanks and especially in the case of the 30L EXT give you an excellent opportunity for Aqua scaping that most smaller tanks do not provide.
As to why BRS does not have them, that I am not sure, maybe
@Bulk Reef Supply might be able to chime in on that...