I am using it. Flashing was kind of a pain. ( See here: Samsung - Galaxy Tab S5e (Wi-Fi) - gts4lvwifi - Documentation Suggestions - #2 by trashHeap and this thread here: How to install /e/os on a Galaxy Tab S5e SM-T720 (TWRP) ) However, it’s been great once I managed to get the OS on it.
Have not tried an external screen with it. Don’t have the dongle. Are they cheap?