They're limited to pretty small sizes by german law - they are so insignificant that they're much less dangerous to handle. I'm not up to date on their ROI, but IIR they usually were a rather bad investment and more of a novel toy than a serious and reliable source of electricity.

Essentially, any notable installation fundamentally deals with much higher currents and voltages and as such is much, much more dangerous. Once a certain size is reached, the carrier also has to be involved and professional installation is mandatory, both due to the law and requirements by insurance companies.

At least here in germany. I've been involved with building all kinds of PV installations in bavaria, from 4kwp up to 20MWp. The balkony generators aren't taken seriously by anybody in the industry right now, at least.