I have very fond memories of this book and it's sequel "Children of the Night", as my first taste of space opera in my teens. Despite their flaws they remain amongst my favourite books.
Cards on the table; "The Space Mavericks" has a (perhaps deserved) reputation for being one of the most badly written books ever (trawl the SF discussion boards and you'll find it mentioned often in this context). And I have to agree there are some toe-curling moments. However, I'm as inclined to blame that on poor editing (of which this book seems to have had none) and amazingly, I'm going to recommend you read it anyway.
This book's great strengths are that it's crammed with interesting ideas and a believable space-trading background. Customs officials need bribing. Spaceships need maintenance. Space traders on shore leave make trouble, so spaceports are surrounded with a seedy strip. Cyberpunk before Gibson if you ask me.
Warp. The description of warp is by far the most interesting I've come across. It has more depth than the usual thinly disguised conceit that just allows FTL travel. It has properties and behaviour that have bearing on the plot. Criticisms on the grounds of "realism" are surely in themselves ludicrous.
Modification. This is an interesting Faustian deal, which I think Kring handles imaginatively. It does make the lead character Fripp Enos rather handy in a bust up, but then I like my heroes to be, well, heroes. And it's a long way from a carte blanche, especially when the ring starts to mess with its function in the second book.
The "magic" ring. Any advanced technology will accept the "magic" brand name from a less developed culture (what would _your_ grandparents have made of mobile phones?). The discovery of a vanished advanced civilisation and all the obvious questions that raises, is the plot arc for the trilogy.
Perhaps this is the cut. This is SF - a literature primarily of ideas - and the ideas are why I love to read SF in the first place. Great writing doesn't guarantee good ideas. "An Enduring Love" and "Lolita" come to mind. Delicious prose undoubtedly, but I hated the books. If you are a "medium, not the message" advocate, don't touch this with an 11ft barge pole. If you can ignore the odd paragraph of duff descriptive prose then there's a lot of fun to be had with the underlying story and its accompanying ideas.
P.S. Nothing of the author has been heard since the early 1980s. Sporadic web searches continue to draw blanks but I for one would love to see the third book published.