I have a thumb throttle made from a shifter. I finally went in and filed down the positions so that i could use it as a continuous throttle. I like it better that way. It still has enough drag to sit in any spot I like.
My bike (see avatar) has a "lawn mower throttle" that's the way it came. I like it because the bike is sooooo slooooow that any ride is a long ride and it's like a cruise control. I don't know if I'd recommend it for beginners or faster bikes though.