Stephen,
The weird shape that you are seening at the edge of the field of view of our 30mm is astigmatism. It is the prime symptom of an optical mismatch between scope and eyepiece. The hardest gem EP to find for Newts is long focal length ultra wide angle. I have not found a cheap 30mm EP that doesn't show a lot of astigmatism. Unless you shell out the big bucks for an Explore Scientific or TV, you will need to tolerate a lot of astigmatism.
A little shorter focal length that is bloody good in Newts, especially at f/5, is the Celestron 23mm Axiom LX. Available now only 2nd hand, but inexpensive (less than $150). The Luminos 23mm is not the same design and does not perform anywhere as well in Newts.
A decent and inexpensive 15mm is the GSO Superview. It will show a little astigmatism, but it is not grotesque at f/5. It is also a really easy EP to use as you don't need to struggle to look into it. People tend to hold onto their Superview eyepieces as they perform really well for their price. Best in slower refractors & in SCTs and Maks, but respectable in Newts if you are on a tight budget.
In short focal length EPs, the Explore Scientific 82° line isn't outrageously expensive, usually less than $200 even new.
If your budget is tight, the TMB Planetary Type 2 line is a bargain! They all have a BIG eye lens (the lens you look into) and all have the same generous eye relief meaning you won't need to park your cornea onto the eye lens to look into them, not even the 2.5mm. They will all do a good job in Newts, but the very best performers are the 7.5mm 7mm, 5mm, .5mm, 4mm and the 2.5mm. These were specifically designed for refractors, but in Newts they do very well. You will find these on Ebay for less than $50 each. Do an Ebay search for "SWA eyepiece".
Other people will be able to recommend other gems for your Newt. But all the same read as much as you can, and learn to identify the clues that indicate optical matching or not. It may be just the one single focal length from an entire line, but that's the gem!
Alex.