My honest opinion is:
You are asking a lot from a $30 bit of kit, especially with your astro experience. You would be better served with binos than this monocular. Even an 80mm f/5 achro would swamp the monocular. I imagine you are considering this monocular to save luggage space, and a few bucks in not taking better astro gear. I really think you'll be disappointed with it. It won't be like you are trying to look through a brick, but for $30, I can't see it being real flash.
A link to one of these monoculars would be a help too.
Is it like one of these?
35X50 Monocular from Ebay
Look at the actual aperture - 42mm, not 50!
Its field of view rating makes no sense at all either. It's claiming a 5degree TFOV at 35X. You can't get that with most 15X50 binos!