I had the Busch & Müller Toplight View mounted on my Brompton and had repetitive reliability issues with it: after riding about on tear with it, no standlight anymore (light goes immediately OFF when stopping). I opened one of the Busch & Müller Toplight View that had the problem and discovered that the issue is the big super-capacity that provide the energy for standlight, its not soldered on the printed circuit board but snapped between the PCB and a metal strip. Th problem is that the super-capacity is relatively heavy and with the vibrations while riding the metal strip doesn't hold the supercap firm enough against the PCB -> bad contact, no standlight anymore.
And its difficult to open the plastic casing of the Busch & Müller Toplight View that is glued without destroying/damaging it.

I have now a SON rear light instead.

For the the Supernova E3 Pro2, its diameter is the same as the E3 Pure 3 but its much deeper, not sure it will fit on the Birdy ?

What case or bag do you have to carry your Birdy?