If you can afford it, the Hudy truer is by far the best truer on the market. The bit alone is worth it's weight in gold; perfect, clean cuts every time.
http://www.hudy.net/xhudy/products/p...7&kategoria=62
A manual truer will work, just make sure you get one with a good bit, or that a Hudy bit will work in. The main benefit of a automatic truer over manual is that it is automatic; turn it on and it does all the work for you, freeing up some time to relax or talk with your friends while at the track.