If you want performance and stability out of your MX400 here are some suggestions:
Change to the MX aluminium head and seesaw with center bearings - I believe thats the 450 upgrade.
Change to the Align feather shaft and the Align Blade grips - aluminium ones work best. Parts are easier to get and better value.
Change to the Align tail boom and mount a digital servo on the boom for rudder. Again two booms in a package - great value.
Set up a Futaba 401 as your gyro - well worth the price.
Change over the entire Tail Rotor system to the Align SE system with aluminium blade grips. You will be very happy you did.
Use the ARK-400 long belt - you can use the stock Align SE belt but I like the ARK long belt - it appears stronger
Use Curtis Youngblood 325 CF Main Blades - they fit perfect and are balanced right out of the box. At least mine were.
I recently received two new TP 2200 Extreme LiPO's...nice very nice.
Finally, make sure that everything is balanced and straight. Main shaft tail shaft everything. People may disagree, I have found that with these smaller heli's a little bend or "a bit" out of balance really magnifies itself.
Some will say, why didn't I just buy a TRex. Well at the time I wasn't sure if this was the path I wanted to take. The original cost of the MX-400 Pro
was too good to pass up. At the time I was thinking a 50 size nitro. But you can't fly that in your livingroom can ya. My CP Blade flys really well too.
This is what I did and haven't look back since.