I had KR8 models before my Reo's. I have used the cartos and Attys. What I like about the Reo when it comes to cartomizers is the convienience. I used to carry 5 batteries, with 5 cartos. I would vape away on them until I got the "marshmellow" taste that tells you your close to burning the carto.
The difference with the reo is that you can consistently feed them and keep them wet. You can run many ml's of juice without ever taking it off the PV. I don't fill multiple cartos every evening, or tons at a time. I also don't carry a bottle to drip top them off. I have run about 15 mls through a carto before it became too stiff, and the taste was off, so then take it off and toss it in the to be cleaned bucket.
I think I know where your coming from with the question, because it wasn't "terrible" filling cartos. I had the same thoughts. But honestly, the Reo won me over. It made it really easy for me, especially with the cartos.
Finally, I did notice a difference when using LR cartomizers in terms of the TH and flavor compared to the higher resistance KR8 cartos.
I hope that helped!