For $45 it looks like it was something worth experimenting with.  Regardless of the product you buy the key factor to keep in mind is does it perform as well as it should in light of how much you paid for it.  This product met its design parameters (or what I can tell them to be) effectively; a cost effective way to put a CAR stock on a remington 870 in that it accomplishes its mission well.

It is interesting watching the development of all these products.  People in similar situations will come up with similar solutions to similar problems all around the same time.  There are currently a total of 7 or 8 companies making AR stock adapter related products for shotguns.  2 of them were released several months before the SST-870, one shortly after, and the rest now more than half a year later.  Looking at all the various designs you can tell that each one is the result of the experiences of the designers, the pool of resources and input they had to draw from, and what "problems" were more important to them to address in the design.

From the start of my design process I had specific requirements that I wanted the SST-870 to meet

1) correct cheek weld for using optics.  This is the primary reason I made the SST-870 for using optics on the shotgun.  If I wasn't a visually challenged shooter that hates using iron sights it would not exist.

2) easier cross training.  I wanted the adapter to mirror the dimensions of the AR15 identically for easier cross-training and so cheek weld and grip remained constant when transitioning between guns at the practical matches I shoot.

3) complete modularity.  Any stock and any grip that will work on an AR15 will also work on the SST-870.  The uncle Mikes QD sling swivel points provide more options for carrying your shotgun.

my part met all the design requirements I laid down for it and it is performing well for the people who bought them understanding the purpose as well as the limitations.  The only real complaints I've heard are 1) lack of iron sights, and 2) the cost.

1) I don't believe to be a design flaw as we always intended to eventually do an iron sight to work with it.  The primary advantage of using an AR stock with correct geometry on a shotgun is the cheek weld to use optics effectively.  The optic I had in mind when I made the SST-870 was the OKO because it is affordable, a good sight, and had BUIS built into it which are more than good enough for shotgun work.  

We are making a front iron sight with increased options for modularity of the system.  Our subcontractors are working on the tooling for them right now, and they should be ready in 4-6 weeks.

2) Cost is a valid issue, and is something that makes the SST-870 not right for everyone.  It is a machined part that is fairly intensive to manufacture though so the cost is somewhat unavoidable.  We will be making a polymer version of the SST series stock adapters that will have many of the same features and options as the aluminum ones, while being priced so the average shooter or hobbyist can afford them.

I have to reiterate I don’t believe everyone needs one of these to use their shotgun effectively.  I made the SST-870 in a large part for myself based upon my experience shooting practical matches in the past 2 years. There are many shooters who can benefit from using it though, they recognize the need for it, and they are buying them.