I'm no expert but having dragged 25 or 30 hardwood trees from 12-30 inch diameter from my homesite this Spring I am experienced.
Dragbar & a decent length of chain with a hook-end work quite well on level ground and with a more or less straight pull. If you turn sharply lugging such a weight you could tip the BX. Seatbelt and brain engaged are requirements.
Trees w/ branches attached aren't so likely to roll, but unbranched short sections of larger trees will tend to roll off to the side rather than drag evenly - somewhat dangerous. I cut one large dead limbless oak ~3ft diameter into 7-8ft sections and rolled/shoved them with the FEL. That was OK for the 400-500 ft I wanted to move them, but a nuisance for longer distances. Most other trees dragged OK in one to 3 pieces. Often if you just get 'em moving you can drag 'em off in a hurry.
I don't know how big your firs are and what sort of terrain you have to navigate, but a drawbar and a chain are a good inexpensive investment IMO (~$60US) for general tractor use anyway. Getting even a small maneuverable tractor in amonst stumps is tricky so I'm not sure how much value the arches and skids are if you can't get the trees into them.
The FEL is also remarkably good at pushing the trees into rough stacks, but lifting/shoving tress from the side at any height can present an unbalanced and shifting load that could tip a tractor in a hurry. Take care.
