I made a new Y mask sized for my 50mm f/1.8 lens(which has a very small objective by the way) and tried it last night. In the moment I did not find the mask helpful at all. I couldn’t see the spikes on my LCD at all but when I uploaded them after focusing by eye I see the spikes perfectly. So, my by-eye focusing worked as well as the mask would have in this instance but the mask is not hopeless. The shot was taken with the lens at f/4 4 seconds ISO 1600. The star showing the spikes is Sirius by the way. Also by the way, when the focus was really off you could see the Y mask in the bloated star. The thumbnail below was taken at f/1.8 1/2 second ISO 6400.
I took a couple of further shots. The best one captures most of Orion. It’s below both original and after stretching it with the Paintshop Pro histogram functions. They were shot at f/4 2 seconds ISO 1600.