The SKAR IX-12 is one of the cheapest 12-inch subwoofers available on the market so I figured I'd give it a shot. No big surprise that it's not great. But, to be fair for $50, it's not terrible either. If you're limited to subwoofers at this price range only then it's worth a shot. Just don't kid yourself about what you're going to get.
Linear excursion (based on 20% THD threshold) clocked in at about 4.1mm one-way. This excursion limiting is caused by the very wide inductance swing from in-to-out. Otherwise, the motor and suspension look reasonable (though, the suspension offset is an issue, it's the least limiting factor here).
My measurements yield an enclosure size much different than that of the manufacturer's for a more neutral response. The manufacturer's recommendation yield a peaky midbass response. Which is probably just fine with the people who are shopping for this.
Still, if it were me, I'd recommend saving a bit more and looking at the $100 price range. Of course, not everyone has that luxury, so if you're limited to $50 this is a reasonable recommendation.
If you do plan on purchasing this subwoofer please consider doing so via my Amazon affiliate link below. It costs you no additional money but does help me with a small 4% commission which helps me pay for more test subjects and hardware to keep this channel going.
Buy: https://amzn.to/3iT8Pdc