If you check out my "Brushless 1/8th Buggy" post (
http://www.rc-monster.com/forum/show...=&threadid=429 ) you'll see that I took a Hyper 7 TQ Sport kit for my brushless conversion. After the time I've spent on it and things I've learned, if I do it again with a 1/8th buggy, I'll consider using the OFNA MBX 80% prebuilt.
The Hyper 7 has a steel spur and no apparent plastic replacement, but the MBX has a steel spur with a direct plastic replacement. The plastic spur for the MBX is wide, as well. This should help with durability of both the pinion and spur.
I've purchased the MBX center diff assembly and am in the process of "forcing" it into my Hyper 7 TQ.
Also, the MBX has quite a few more easily adjustable pieces that the Hyper 7 TQ does not. You can compare the two at OFNA's website.
As far as performance of the chassis, I've read that the Hyper 7 TQ is more race-worthy than the MBX, but it doesn't sound like you'll be racing anyway. Both models have pretty equal parts availability.
I think the only things you get with the Hyper 7 TQ that you don't get with the MBX 80% prebuilt are the body and tuned pipe.
It looks like it may be more work to put electric into the MBX since the online photos make the chassis setup look more crowded, but that may be remedied with a good dremelling anyway.
Lastly, the MBX 80% prebuilt is about $100 less depending on where you purchase.
If I compare my experience in cost this far with what it could have been with the MBX as my initial purchase, I figure I could have saved about $200. I've had to purchase a MBX center diff and spur gear, as well as purchase the more expensive hardened steel pinions (5mm), plus the initial $100 more for the kit.