Hi Nagga's
I have the roof mounted on my 14.44.4 OB and have no problems with lifting the roof (I'm no tall muscle man), Don't worry about roof strength as they are made to cope with roof A/C units.
I personally like the way the roof units distribute the air around the van compared to wall units which I think tend to blow it straight at you. You also keep the noise up high on the outside and also finish up with more cupboard /storage space.
I also have no problem fitting my van cover with the roof a/c.
Yes the downside may storage height for some people.
Great thing about the forum is you will get lots of good ideas and opinions from members experiences with their Expanda's
Good luck with the research