As always you have to a lot of reading between the lines of reviews and consider the possible sources. Customers of inexpensive subs are likely to be non-audiophiles, probably young gamers/action movie buffs, or inexperienced and proud papa sub owners that are making their first move up from an all in one box A/V system. Is that who you want to take advice from?
There's a reason why good subs cost more (aside from simple greed), it's called the laws of physics and it applies more directly to subs than any other audio component. Deep bass means pushing lots of air and the bigger the room, the more air needs to be pushed. And to have more than mushy one note boom-boom, the components and design must be of good nick. The advent of class D amps and servo control have helped reduce cost/improve subwoofer quality in recent years, but quality drivers, well built cabinets, and shipping costs are givens.
as often is, JLM for president
IMHO plus you crack me up laughing, are you sure your not a pissed off therapist.
I used to think of sub wolfers
as tumors and furniture, truly, and akin to a personality type I did not trust for a whole lot of deep stuff,
but D switching Woofer amps are so frigging tight and fast, and no clipping
that they can now often be added now without sounding like your system has 19 cross overs and can have real tone down in the lows.
look for a used "REL" they have a interesting technology and can fall off a truck and still be fine.