All three are excellent bullet proof wheels.
Most of the differences are minor and only affect the weight of the wheels. The Zonda uses a cheaper milling process than the Eurus and Shamal adding a little weight. The Zonda also uses SS spokes and brass nipples compared to aluminum spokes and nipples on the Eurus and Shamal. The Shamal does have carbon fiber hubs and different bearings reducing weight even more.
As far as is it worth it to get the Shamal's, well what is your budget and how important is weight to you?
You can't go wrong with any of them. I just sold my bike that had the Eurus's and I put well over 10,000 rough miles on them and never did a thing to them and they still rolled like they were new. I ride with a guy who has the Shamals and the hubs are sexy.
I would buy the Shamal's if they fit your budget but wouldn't regret the Zonda's