Just at a quick glance of t he Husqvarna site:
It appears that the "bt" and "bf" are just designators of the throttle location.
BT- tube mounted
http://www.husqvarna.com/us/products/leaf-blowers/350bt/965877502/
BF - frame mounted.
http://www.husqvarna.com/us/products/leaf-blowers/350bf/965877701/
You'll want to check if the tube throttle has a way to set/hold the throttle at whatever desired speed, you need.
Having to constantly squeeze a trigger, as you move leaves
will get tiresome rapidly!
I've only run my Echo units, Thus I can Not speak to the ergonomics of the Huskys.
But I much prefer the tube throttle.
I like the trigger action on the hand grip vs the friction set lever on the arm type throttle.
I think it's Handier, easier to control when working around the yard.
You have a free hand for grabbing limbs or vines or carrying something.
Remember, this is an Echo unit. The Husky may be just great!
With the throttle arm up, I find that I hang up the throttle arm inside the strap, when slipping the blower over my shoulders, about half the times I grab it.
But this is all just a matter of how I pick it up and try to slip into it.
Someone else may *never* have it happen to them.