I own a Catrike 700, which is more of a "racing" trike, per se, however I use it only on roads and have used it on gravel roads (that was some tough biking, but it was too with a Catrike Speed of my uncle's).  I love my 700, but I rode all of the models that were available to me (including other brands) and found the 700 to be the most comfortable for me.  I definately think a front deraileur is important as some of the climbing I've done wouldn't be possible without it.  I would try all the models available to you before you purchase.

K