I have BLS255/256 on one E7se and RJX FS0521/FS0521T on another E7se. The Futaba are certainly a better over all servo. Much more power friendly, center a bit better and are much friendlier on BECs. That being said, for the cost difference, I am VERY satisfied with my RJX. I even put a set on my new N7 kit.
When I say the RJX aren't BEC friendly what I mean is they have a VERY steep ramp up on first power on. This is often more than the BEC can keep up with and one or more of the servos won't initialize. Its a simple matter of powering down and back on in most cases, but if you run straight RX lipos like I prefer to, this is a none issue. Please note, I have never had a RJX servo shut down a BEC in flight, the power ramp is only on first power on.
As for Coreless versus Brushless., I have yet to have a set of servos go bad from use so I can't offer any longevity comparisons. As for power consumption I can say this. My N7 with RJX gets 5-7 flights (depending on ambient temp) on a single charge of my 2s 4000mAh Gens Ace RX lipo. Darren Lee has the the BLS255/256 servos on his N7 and boasts 10 flights on his 4000mAh Gens Ace RX pack. That's a pretty significant power difference.
I have ran MKS and Torq servos in the past, for the money get the Futaba in my mind. Their cases are none-standard and require shimming. They are also a bit more power hungry. If you are going to spend at that level, I would recommend the Futaba. Just simpler, but that is my opinion.
I hope this helps!
