Before you buy one, think about what you might connect to it down the road. The RKL is limited to 4 modules but the RKE can handle 63 ( I think ).
I have a 75g with 110g total.
I bought the RKL @ Christmas, and by mid-Feb I started looking @ the RKE because I wanted more than 4 modules. It started when I wanted to have more than 2 PC4s and thought one Moonlight controller may not be enough if I wanted to have all 3 colors and enough intensity. Then I started thinking about connecting everything to it. My current hardware list is fairly large;
Eheim 1262 x 2
Skimmer
UV
Heaters
Chiller
Chaeto light
Lighting fans
Lights x 4
I currently have 3 PC4s, an SL1 and a Moonlight controller ( plus a hub for ease of connections, but it doesn't count as a module ).
I have future plans for more modules, but you get the idea.

Exactly what I am ending up doing, once the live rock is cured.

I just ordered an Apex with 2 8 outlet bars and 1 4 outlet bar, all the regular probes, switches, and floats as well for my 200G build.

I try to buy things once, upgrades are expensive, and I know I will want to upgrade sooner or later, I always do.

Without even much thought the tally of items adds up pretty quick...

8 outlet #1
Return pump
Closed loop pump
Refugium feed pump
Refugium lights
Sump heater 1
Sump heater 2
Protein skimmer
Sump/cabinet light

8 outlet #2
Lights 1??
Lights 2??
Lights 3??
Moon lights
Only 4 spare to start...

What about:
ATO??
UV??
Dosers??
Reactors??
Auto-Feeder??
Additional power heads??
Yet to be invented must haves??


4 outlet (mixing station)
Mixing/water change pump
Heater
RO/DI
Only 1 spare to start...

Already at 3 15A circuits as well...

i see your points but my way of thinking is

module 1 heaters
module 2 return and CL pumps
module 3 powerheads for wave actions
dont run UV, ATO,auto feeds, electronic reactors
i see no reason for my dosing pump skimmer, cabinet light to run thru a controller unless it was connected to the internet which in turn to my pho ne..........unless im missing something but that to ne isnt worth the extra few hundred bux
i can plug a power bar into an outlet for 2 heaters controlled together
powerbar for pumps controlled together
my mixing station is nowhere near the tank so they would never get plugged into it

i still have an extra module left

Ya, I hear ya. There are many ways to set up a tank. I'm looking forward to the history log and safe guard alarms that you can do if everything is tied in to the controller.

true

thanks for your input

Im gonna order it and see how I like it and if I decide id like more options with a controller Im only out $130 on this 1 and I can spend the difference on livestock!

True enough, that's a good way to look at it

This you don't get with the DA stuff e46er, just so you know
The Apex units are more advanced
I went with DA as the Apex units didn't suit my desires, but I still spent almost as much

The RKL has data log which shows min max and avg....... What else for history would u want?

It doesn't log for as long as the Apex is all I meant
Me thinks you only get an hour with the DA
Either way, it wasn't on my list