Actually, there are only two diff Align Trex 450's being built today. The previous version was the 450 SEv2 which is a proven machine and still available in clone form.

Today, Align makes the [link=http://www.align.com.tw/shop/product_info.php?cPath=22_25&products_id=2886]Trex 450 Sport[/link] which has a belt driven tail and with double stacked side frames. The Belt driven tail is said to offer a little more forgiveness to the rookie pilot with regard to tail strikes and the frame setup provides ample space for electronics. This can be purchased in Kit (w/motor and esc) and Super combo form (w/everything except RX)

The second version offered by Align is the [link=http://www.align.com.tw/shop/product_info.php?cPath=22_25&products_id=2725]450 Pro[/link] which has a single piece side frame and torque tube driven tail rotor. It has less space for electrics but the single piece side frames offer more rigidity to the overall heli and hold up very well in the event of a crash. I have not flown a Sport but I can say the Pro tail holding ability is better than the SEv2. The Pro can also be ordered in the Kit or Super Combo kits.