Subcompacts are more sensitive to the quality of the transmission/hydraulic fluid than larger tractors. They have to dissipate a lot of heat, and have good low temperature flow. Low quality fluid (that might meet spec) may have it puking out the hydro fluid when the filter ruptures on a cold winter start up. Or a really annoying whine, and loss of power when used in hot weather. The higher cost of the premium oils is partly due the additive packages that have all the goodies that enhance and extend the service life the oil. You might be able to find a $40, 5 gallon pail that meets the standard, but how much are you really saving in the long run?