Good choice to go with the 401! It should last a long time.
It is one of the most liked, popular, and supported gyros on the market.

You should mount it under the tail boom mount to protect it from a crash.
If it is mounted on the top the flybar paddles can crush it in a crash...

There was a 401 for sale like new with box and instructions on this site for $85 shipped.
Some others were $90-105 shipped.

Are you a member on helifreak.com?
I am and have all of the videos downloaded for the T-Rex 450.

There is a very good step by step setup video with the 401 gyro on a T-Rex 450.

401 gyro setup (48 Megs)

http://helifreak.com/showthread.php?t=11373


Tom