I reckon if you can afford the HX go for it. You will never regret it. I have had my Diadema for nearly a year now and it has been an absolute joy to use. It really comes into its own though when friends arrive - endless amounts of steam, consistently good espresso and easy to use.
One word of advice - buy from a good dealer. When I picked up my machine I got a three hour lesson that Im sure saved me hours of headache trying to work things out for myself!