oh hey
I'm in a similar position - I've had my Tab S 8.4 since it launched 2014, and since the S2 came out as 4:3 I've been looking for a "better" tablet, and not been able to find one.
(Why do Samsung always do this - First Galaxy Note 16:10, everything else 16:9, first Galaxy Tab S 16:10, everything else 4:3, why, why, WHY)
Reading a lot of reviews and opinions on this M3 when the S3 came out, didn't leave me overly impressed. But it's nearly 2018 and there STILL isn't a better tablet (eye heart amoled), and this is the closest it comes if you want an 8.4 inch, 16:10 Tablet that takes SD cards. 32GB & 3GB RAM is starting to ware thin so I'm going to take the plunge. Wish me luck.
EDIT: Actually, scratch that. I'm used to (circa-2010) HTC and current Samsung forums full of roms and changes - there doesn't even seem to be any customs ROMs for this tablet? If we hit Jan 2019 and this is still the only option, then I'll go for this. I seriously hope not.