I've used both, and own a Crossbow Platinum. While the Boxflex feels a little more solid (craftsmanship, durabilty, etc), the Crossbow has several advantages over it. For me it was a no-brainer as to which one to get. The Crossbow:
- costs way less
- has a huge edge in range of motion (might not seem like a big deal, but you'll soon realize otherwise)
- can change weights in a fraction of a time (great for cardio-circuit training - you want to get into your next set quickly)
- looks better, IMO
- counts reps for you, which I really like because keeping track of them in my head rather annoys me. This way I can better concentrate on my form during the reps.