I don't have any experience with the XOP I beam. If you can shorten the beam without compromising it's structural integrity, I would say go with the i-beam. That way you don't have to worry about reinforcing your aluminum tube. On the other hand, the aluminum is apparently a lot cheaper (according to BB) and reinforcing it is pretty easy.
As far as working with the aluminum tubing, it's pretty easy. I cut it to length with a regular old hacksaw and drilled the holes with a Dewalt hand drill. No special tools required at all. Finally, give it a quick camo job with a rattle can or use some camo tape to dull the shine. It's actually a pretty simple process. The hardest part is finding a seat!
The price must have changed, or maybe I linked to a different product. I paid about $12. That was the first time I had ever bought aluminum tubing, so I didn't really know either way.