The Roku 3 supports FAT16, FAT32, NTFS and HFS+ drive formats. My guess is that your other devices only support FAT32? That would make the maximum volume size 2 TB for FAT32, IIRC. Assuming full implementation of NTFS and HFS+, your drive should work. I'd check with Roku first, though. Also, I have no trust of USB standards implementation, so I always use external power on something like hard drives, and I swap out the wall warts every 5 years or so (lost the greatest phone ever made to a bad wall wart).
To the A.C. troll below, I would say that, yes, there are additional products to accomplish the same purpose, but the Roku is best device of all those devices. Given Roku's business model of not requiring to get between content providers and viewers, and their excellent record of updating firmware for old devices, I expect that the Roku is the best value for some time to come.