I am fairly sure the Kress uses a fairly basic triac switching speed control. One of the functions of the speed controller is to ramp up, rather than an abrupt start. I don't know about the SSR you mention, but the ones I use for furnace control are very much on/off switches, switching at zero crossing.

Basically, I am saying ; exercise caution as it could cost you a Kress 1050.

Cheers,

Rob