I personally think it would be ok. With a six foot tank there will be plenty of space for them to avoid each other. I would get at least 3 females though as the male will wear just out when breeding.
As for them likeing small spaces. Why would this be? He'll just find a nice quiet spot and stay there most of the time. I have one in my 3 1/2 foot tank and he sits on top of the filter where there's no current most of the time.
Thanks for you replies. I will go ahead and get one now i know its ok.
Also can i ask how people have decided that bettas like being in such a small space. my betta is a very happy fishy and has had no problems in my tank.