Im switching 12v solenoids at about 1.5 amps about every 20 seconds. i had to move on from relays because the contacts fail after a whileso a mosfet seemed more logical. i was only worried about flyback spikes when de energizing the coil but the green mosfet boards not only includes diodes but also the optocouplers. i dont really care if there are optocouplers or not. i just dont want any CPU crashes etc.
in the testing environment i used a freq generator to switch the mosfet quickly with a load on it without issues, i was also able to switch the load at 50ms on 50ms off intervals for a half hour with the pcf8574 and bypassed optocouplers still had no problem. i don't think you can even really buy all those components for less than they are selling the boards for