I converted my MBX6tr into an brushless racing beast. I have ran it over and over and over on the track. I have done this conversion on both my Mugen 6's.
Pros, the aluminum parts are on point and battery tray is really nice. It fits any size battery you want.
Cons, the ESC mounting area is not able to use double sided tape (you know, what you use in all other applications) Nothing sticks to this plastic material. I used Hobbywing XR8 ESC, which comes with mounts.
This is not really an con. I just wish the center diff/motor mount was a 2-piece. I really dislike removing the whole motor mount to service the center differential. *YOU MUST USE LOCK TIGHT ON THIS MOUNT. I have lost the 2 screws twice now during an race and I always am checking tightness.

This is my 2-cents.

I refer everyone to RC monster.

If you have a Mugen MBX6 gas car and want an electric and can’t make up your mind whether to go with an Mugen ECO or the RC Monster Conversion, go with the Monster and save a ton of money. I used the RC-Monster brushless vehicle setup guide! And the gearing was spot on, I run the gear they recommended and haven’t changed it yet and the car is AWESOME. I get 18.5 minutes hard run time on a 5800mah lipo using the gearing they recommended for my motor spedo. setup. These guys at RC monster know there stuff and the conversion kit had great craftsmanship and it fit like a glove.

The craftmanship of the kit is fantastic and fitment practically assembles itself. The material is clean cut light and strong, great skills Mike for the CNC process.