Hi Dusty - yes I do mean one of those. Nice to know you can use a search engine
Both machines have their own benefits but I would not tackle a greasy kitchen floor with steam alone.
The Rotowash, being the most expensive but probably the most durable is an excellent machine - but cannot get right up to the edge. The Duplex will go right up to the edge.
We clean alot of altro flooring using a Rotowash. I suggest you use a degreaser such as Champion or Dynax, allow dwell time giving the chemical a chance to work on the grease and then start machining the floor -
with the dirty water tray removed. This allows you to agitate the surface without drying it. Work the floor north to south, then east to west several times over and then put the tray back in place making further passes to remove the slurry.
You may then want to repeat the process using clean water as a final rinse. The whole process is very similar to carpet cleaning.
If you look on the Used Equipment section on this forum there is a Rotowash R3 for sale at a snip at £350!
Without knowing the size of the kitchen it is difficult to comment but I would guess that the R3 would be sufficient.
This is premium rate stuff and if I was doing this overnight I would be looking to charge around £100 per hour.
Good luck.
Musicman