You can control turn on by programming it and telling it when to come on ahead of time. But no, I don't think you can press a button and make it come on automatically while driving.
used one at work, gonna be using another one soon (typically we deal with aircooled cars here) the only thing i wish the Spal unit had, was a way to clear athe 50% turn on and Full speed turn on point, which i myself (maybe it's only me) found to be fun setting the 50% turn on point, if you want it to turn on alittle later then the factory point.. (and also raise the Full turn on to) since the two points then become `to close', it has a hissy fit, shuts off and starts flashing it's lights at you.. but found, it just to fun to set, but can be done, and is pretty good, so far (one year with one installed, and no problems yet (knock on wood) compared to the Flex-a-lite VSC POS i have in my own car)
Also the other thing i like about the SPal unit, is you can have a primary fan and a Secondary fan.. the Primary wil be Variable speed, and if the temps still climb to the full speed part, it'll turn on a second fan (full speed only VIA a relay)
witht he Spal, the only thing is i wish one can earse the turn on points fully, would be, least to me, easier to program..