we have one -- wifey loves it, in particular to de-stress and break a winter chill.
my only advice is to get one bigger than you need. we have a "2 person" unit and its pretty cozy for 1 grown man..IMO a 3--person deal is the minimum of you want to have some comfort.
personally I don't get saunas...why sit passively in a pool of your own sweat when u can get the same while also exercising?!?!
here's ours:
