The 18 means 18 grams per hour.
The 35 means pool size 35,000 gallons.
They both produce the same amount of chlorine. The output is about 17.5 grams per hour which is 420 grams per day or 0.926 lbs.
The ei18 is for 50 hz power in places like Australia. The ei35 is for 60 hz power in places like the USA.
So, they are basically the same unit other than the power input.
SWG chlorine production