this one I know how to answer..

manual regulator - CO2 being release 24hr a day ( not too good at night for the fishes ), CO2 finish faster...

soleniod regulator - CO2 is turn off at night with a switch timer ( Ikea timer RM9.90 ) when no electricity is supplied to the regulator, so no CO2 gas is release at night..

Manual regulator is around RM80-RM100...

So with the extra RM200 you pay for the regulator, you can refill the gass around 5-10 times... plus more exercise of carrying the heavy CO2 cylinder to the shop every 3 to 6 months..