Sure. Allthough they have their downsides, it's quite handy when you don't have to worry about navigation, style & layout, event handling etc. Just create the widget and add it to an HContainer, simple as that.
HAVi widgets are not being used in Belgium MHP deployement.
Tests in the past have shown that interoperability across different implementation of havi widgets cannot be garanteed.
Apart from havi widgets, some other havi api's are also used for other things like Hscene, HBackground.
These are essential and used by most (if not by all) xlets.
In the mean time havi widgets are now optional in GEM 1.2.2. But they remain mandatory in MHP 1.2.2.
Why are they still mandatory in MHP 1.2.2 ? And could one make a MHP 1.2.2 implementation without havi widgets ?