TLDR version;
I have Bots/Traps/Mu and I find it works great.
Long Version;
The max width of the tentacle cone should be around 17.7356 units while the diameter of the mu sphere is 20 units, though the cone has a slightly greater area overall to fit mobs into. The -KB is the deciding factor though, I found it made me a vastly more efficient damage dealer when mobs are not scattering after the missile burn patches are dropped. Numbers below:
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Electrifying Fences
Level 44
Type Click
PvE damage scale 0.800000
Accuracy 1
Modes required
Modes disallowed Disable_All, Disable_Pool, Disable_Epic
Range 40 feet
Activate period -
Interrupt time -
Cast time 1.17 seconds
Recharge time 20 seconds
Endurance cost 12.74
Attack types AOE_Attack, Energy_Attack
Effect area Sphere
Radius 10 feet
Arc -
Max targets hit 10
Entities affected Foe
Entities autohit
Target Foe
Target visibility Line of Sight
Nofity Mobs Always
Target:
* 8 * 3.06 Energy damage over 7.10 seconds PvE only
* +17.88s Immobilize (mag 3) PvE only
* 8 * 11.65 Energy damage over 7.21 seconds If target is a player
* +2s Immobilize (mag 3) If target is a player
Suppressed when Held, for 15 seconds (WhenInactive)
Suppressed when Sleep, for 15 seconds (WhenInactive)
Suppressed when Stunned, for 15 seconds (WhenInactive)
Suppressed when Immobilized, for 15 seconds (WhenInactive)
Suppressed when Terrorized, for 15 seconds (WhenInactive)
* Endurance -0.04 for 6.2s PvE only
* -1 Endurance for 6.2s If target is a player
* RES(Knockback, Knockup) +10000% for 15s [Ignores Enhancements & Buffs] [Non-resistable]
* -100 Knockback, Knockup for 15s [Non-resistable]
* Recovery -1 for 2s (20% chance)
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Soul Tentacles
Level 44
Type Click
PvE damage scale 0.935000
Accuracy 1
Modes required
Modes disallowed Disable_All, Disable_Pool, Disable_Epic
Range 40 feet
Activate period -
Interrupt time -
Cast time 1.67 seconds
Recharge time 20 seconds
Endurance cost 12.74
Attack types AOE_Attack, Negative_Energy_Attack, Smashing_Attack
Effect area Cone
Radius 40 feet
Arc 25 degrees
Max targets hit 10
Entities affected Foe
Entities autohit
Target Foe
Target visibility Line of Sight
Nofity Mobs Always
Target:
* 8 * 3.06 Smashing damage over 7.10 seconds (after 1 second delay) PvE only
* 4.13 Negative damage PvE only
* 8 * 5.44 Smashing damage over 7.10 seconds (after 1 second delay) If target is a player
* 7.09 Negative damage If target is a player
* +17.88s Immobilize (mag 3) PvE only
* +2s Immobilize (mag 3) If target is a player
Suppressed when Held, for 15 seconds (WhenInactive)
Suppressed when Sleep, for 15 seconds (WhenInactive)
Suppressed when Stunned, for 15 seconds (WhenInactive)
Suppressed when Immobilized, for 15 seconds (WhenInactive)
Suppressed when Terrorized, for 15 seconds (WhenInactive)
Thanks for the reply Manic. I'll give it a try and see how wrangling AVs goes with it. I'm sure that regular gameplay will benefit from it immensely. 
Just a quick update if anyone else is wondering about this choice. I respecced today and the benefits are without a downside. Even my concern about herding multiple AVs was unfounded. I coralled Staes and Ms. Liberty just fine. In fact I would say it was easier with the Scirocco's pool.
It's just come to my attention that I can respec out of my Patron choice.
I know I know. I shoulda known this.
So here's my question. Currently I have a Bot/Dark 50 that is a powerhouse. When deciding on my patron I was up in the air about it. Waffling between Ghost Widow and Scirocco. All I really wanted was an Immobilize for AV fights and either fit the bill. I settled on GW and have enjoyed great success with my MM.
What I didn't know was that Scirocco's Immobilize will actually hold the targets still when they would normallly suffer knockback! You know robots..knockback..bad guys thrown out of Tar Patch.
Sooooo now I am seriously thinking about going Mu. What I wanna know is how does the 10 foot radius compare to the 40' cone with the 25" arc? With a little work I can corral 3 AVs into the cone and get them all immobilized. Will the Electrifying Fences work similarly? I can't really visualize it very well. A 10 foot radius would actually be a 20 foot circle and that seems adequate but I'd like some feedback with people who have used the power please.