@tronaton: The RunCam Swift Mini is nice. It's essentially the same size as the old Owl v1. However, I'm afraid it would still be a bit large and heavy for a 2.5" brushless quad. Some have mounted it on the 3" Atom with a custom 3D printed canopy.
I got one with the 2.1mm lens (all that RMRC had) for my 4" Lilith, still to be completed. Nice to see that GetFPV is selling the 2.5mm lens version. There's also a 2.8mm lens, which might be good for dedicated tunnel racers.