The one picture that is dark looks good in the light. I think that’s just how it looks laying on the table. The camera I have only has time and instant for exposure time. I think I had it on a smaller aperture
It's more likely the shutter didn't open at all in that case .
Unless you used a very slow film and shot in the dark , something would show up .
Don't forget when this camera was made all that was available is what we consider slow film .
So if the only shutter speed is about 1/30 second , you should have still ended up with an image .
Not necessarily a good one , but not a blank piece of film .
I use an Ensign Ful-Vue that also has just instantaneous or trip for shutter speeds .
That wasn't working well , so I stripped it down , cleaned it , and lubricated it with the graphite of a pencil , and it works great again .
Summer I use Ilford FP-4 in it , winter it gets HP-5 .
Exposure is what it is !
It's rare that I don't get a useable negative .
If it's really low light , I hold it on a solid surface and use the trip function.