When smoothing textured ceilings I generally will drop the floor with plastic rather than use the tool you are looking for. I use a 6" or 10" mudding knife to scrap the ceiling (depending on how hard the substance is to remove.) Anther little trick is to use a bug sprayer and LIGHTLY mist the ceiling, letting it sit for a few minutes then scraping. Be careful not to let drop into your eyes, I then will skim the ceiling with regular joint compound, then sand and apply prefered texture. After sanding remove the dust with a broom or damp sponge for better adhesion. If you are going with a slick ceiling, be sure to sand out all grooves and touch up any bad spots, or you will see them after painting.

Also, with the texture you described, most of the time it is painted over (unlike blown acoustic) in this case misting it may not work, I would scrap it with a 6" tapeing knife (a good one, not flimsy) then sand with a low grit paper (60 or 40), you can get a sanding pole for about $14, then remove dust and skim with a 12" taping knife and pan.

When skimming, start in a corner of one side of the room, work your way across. When you reach the other side, move over and always skim "into" the fresh mud, don't start your knife in the wet mud on the ceiling. This will take practice, and always put the mud in a 5 gallon bucket and keep it wiped down, little dried particles of mud will case ill effects in your work. When finished for the day wipe down the sides of the bucket with a wet rag until clean(do not scrape) and cover mud completely with water. Pour off the water and remix the mud the next time you are ready to use.