Another plus point of the economy saw is that in general they are very heavily built which considering they are fairly cheap to buy is quite surprising, most that I have seen are sturdily built with a heavy duty cast iron work table, this in my opinion is a 'plus' point because a heavy saw I would imagine is less likely to vibrate than a lightly made one.
Also many of the single speed cheap saws feature small induction motors which in general are the most reliable kind of motor, not only do induction motors offer quiet smooth running they rarely give any trouble for the life of the machine. Models that feature variable speed control on these economy saws are normally fitted with so called DC motors which are series wound - carbon brush type motors which tend to be less reliable and are more likely to vibrate and run nosier than the induction motors, although I am in favour of having variable speed. it is possible to have speed control with an induction motor but the electronics is more involved and expensive and normally only used on high end saws.