The only major con for me is that it takes a lot of RAM.The laptop only has like 4GB so I can barely run my work and 'other work' VMs side by side. Often one will not boot due to memory constraints.
I think it would be fine on a 16GB laptop. I just can't be bothered upgrading that old hunk of junk.
I will bring Qubes over to my next laptop, if I ever do end up getting one. I find it indispensable for traveling - isolating network/proxy VMs from each other is amazing!
I'd also like to run i3 on it as the main WM. I think it is possible with some trickery but I didn't try.