Has anyone seen or have an opinion on this scope?

You're better off saving $20 buying direct from Crosman with the AGN 25% off discount code. $28.50 order Friday to get free shipping Fridays.

40mm vs 50mm for a 3-9x shouldnt matter much.

https://www.crosman.com/optics/scopes/3-9x40-mm-centerpoint-tag-scope-4625

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I have no experience with that particular scope, but it looks like it doesn't have a parallax or focus adjustment. An adjustable objective or side focus scope would be a better choice for close-range airgun use as most fixed parallax scopes are set for 50 or 100 yards. UTG/Leapers has a lot of airgun designed scopes, though nothing for under $40. 

If you do end up buying from Crosman, the discount code is AGNATION. Put it in at checkout and remember there's free shipping on Fridays. 
 
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