Travelling with the 8" Dome is a PITA!!!
But i love it when it produces 50/50s ...
another plus point is that, most curious critters and the occasional fishy comes real close to catch a glimpse of their own reflection in the dome..hopefully its not a nesting Trigger. (underwater creature portraits come impromptu sumtimes)... =)
In my opinion, if you're worried for the cost, then go for the flat ports.
If you want a long-term investment go for the domes, (but mind u, transporting them is err kinda :sweat