I only know the 15-30x50 Gold Ring Compact by reputation - which is fantastic.
I own the 10-20x40 Gold Ring Compact and it is an absolutely wonderful little glass. It is uncannily bright, gives very clear images, and really challenges a person's preconceived notions of what should be possible to accomplish with such a diminutive little item. I am sure that part of this is due to the fact that its small size means that it is always with me. It is truly, incredibly small and yet very, very useful. It is not, of course, a replacement for a good, full-sized spotting scope (especially at dawn and/or dusk) but, when hiking around rough country, it is a real dream.
It can be used hand-held with surprising utility and of course, on a small tripod it really shines. At 20x, you will find things that simply can't be seen with binoculars. I used it last year on a hunting trip in some incredibly steep terrain to spot elk at distances that binoculars simply couldn't handle - which was good because we ended up going after those elk and one of them now fills my freezer.
The 15-30x50 would, I imagine, provide similar levels of performance. It is somewhat larger than mine and in fact, would be both large and powerful enough to reasonably serve as an only spotting scope for a hunter who is not super interested in bird-watching, digiscoping, etc. It won't out-perform larger 60, 70 & 80mm scopes but, you'll take it places where you would never dream of packing those larger units.
Edited by lucznik