I prefer pro armor but any of them on ebay will do. They have some made of a polymer now, they're really cool. I have an aluminum one on mine, but a polymer will be next. With the rearend, just make sure it's 1/4 material.
My rekluse zstart pro was 600. They have a different style that uses some funky clutch plates, but they're even more expensive.
The zstart pro comes with ball bearings, if you want the clutch to lock up quicker, you can install the included heavier tungsten balls.
The trails are a blast, but when you get to a spot where the jeeps get stuck, you'll have to use some fancy clutchwork to get over it. The auto clutch makes those technical spots lots more fun.
Zero loss of power. My launch times are faster now at the dragstrips.
Hope that helps