I got a CZ Woodcock Mini 410/410 from Derrick last year and really like the gun... While I have seen some reason for concern with larger gauge Turkish doubles I doubt the 410 is an action stretcher...
It's not "frame stretching" that is the problem (though the 410 operates at a much higher pressure than the 12 ga except maybe the 3.5" shells and it is the amount of pressure that can contributes to frame stretching) but the wearing of internal parts that is the problem. To get such a low price point corners must be cut and part of that equation is the quality of steel used.
Typically, the wear surfaces are case hardened in these instances and then the longevity is dependent on how well administered the process, the thickness of the hardening, the underlying hardness of the steel, and how well the parts fit together. Amount of use is a variable as heavy use will lead to replacement sooner but that is a gamble as a gun at the low end of the quality spectrum will still break after little use-it will just be a longer time by the calendar. On the other hand, if all went well, a low price point gun may give a long time of hard use.
Some parts may be easy to repair, if you can get the parts, but some items such as pivot points are much harder and very costly to repair. Berettas are designed for replacement of pivot points and they run in the area of $300 to replace last I saw a few years ago. And that is after many tens, if not hundreds of thousands of rounds going down the barrel.
Regulating barrels so they shoot relatively together is also a significant cost. It is more complex than pointing a laser down the barrels and then soldering them together. There are a number of steps to get a decently regulated set of barrels and that costs time and money. The big manufacturers lessen the time and effort through strict quality control of the materials, processing and assembly but even they have a few dogs slip by.
Another factor leading to suspicion of low price point items is quality control. The higher the standards and the more frequent the checks, the higher the cost of production as this leads to more rejects and/or time fixing errors. Low priced items tend to do less in depth inspections as well as less frequent inspections allowing for more potential problems to pass.
Figure in the shelf price includes a 5% mark up for dealer profit, 11% for Pittman-Robertson tax, likely 5% profit for the manufacturer, and what is left has to cover materials, labor, rejects, loss, shipping, advertising, depreciation of equipment, and whatever other expenses are involved and one sees there are numerous corners being cut.
I have been bitten by price point firearms many more times than not and I have seen many, many others have similar experiences. There is a saying that goes something like, "Only rich men can afford low quality as only the rich can afford regular replacement." I have had guns sit in the corner for years due to broken parts that were unavailable and the price to have them made was much more than the value of the gun. Thankfully, Numrich Arms will take them though only for pennies on the dollar. Ship 4-5 at a time as shipping will often eat up the price of at least one gun. I understand finances but always buy the best quality one can afford. In the case of shotguns that may mean a pump or semiauto rather than an O/U or SxS for a given amount of money but one will end up further ahead in the long run.