_ is typically used to i18n strings with gettext, it seems like poor naming for a layout-related function like a spacer.
Apart from that, this seems to be a wrapper on top of PySide/QT to speed up development of basic forms. I don't find it particularly attractive, I have a feeling one will have to drop into QT as soon as requirements get slightly complex. Then again, if it gets more people to approach QT and desktop GUIs in general, it's welcome.