fan controller question

[FitoPharmer]

I have a 6" ~600 CFM 115w inline fan I am using to vent my new fish room. I was wondering if I can use one of these to control the speed of my fan:
Dimmer switch
Or will I have to use something like this:
Speedster fan controller

I would like to use the switch because it will look cleaner, I have an extra slot left in a 2 gang box I would like to fill, and it is slightly cheaper. I have no idea about electronic though, I was told by others it was a bad idea since AC motors do not like variable current. If that is the case then I would imagine the speedster fan controller would not work either.