May be - not. I know 2 kinds of widget:
I am using Trading Signal widget and ity works on my blog with not a problem.
I installed widget (Top Signals) for my google blog in easy way using this link for example so everybody can do it (widget for some particular signal or signals, or widget for some broker). I did not place it on some other websites because I am not a signal provider and I am not market vendor. But I think that google blogs' promotion as a widget (together with simple promotion using facebook, twitter and google+) are fully enough to get some subscribers/clients.
But if some signal provider (or Market vendor) wants to get many subscribers/clients so it may be necessary to go to more quick way - go to the other Metatrader forums to promote your signal or product in direct way - just my experience.
And calendar widget: Add the new Economic Calendar widget to your website for free!