I've just completed my first major harvest of crops since purchasing the fertilizer tool. Everything worked well and my storage is now full of bumper (double) harvests - shortages of things like tomatoes, wheat, and corn are now a thing of the past.
I paid $10 real money to purchase the FC needed - the cost of one trip to the cinema or a couple of visits to Maccas - far as I'm concerned it's money well spent given the time I spend enjoying FarmTown
A 6th farm (or more) would still be nice, but congrats to the devs for such a great new enhancement to game play!