i have had 3 zen tanks (not Zen d109) never had a any problems in any way. i have had the Zen d109 in my hand and its a VERY light/short tank, put a myth reg on it and you have a winner.
you should know the Zen d109 dose not come with a reg STOCK so you think it cheap but you need to buy a reg, then its not so cheap, some shop bundle a cheap reg in with it.