There has always been a lot of conflicting advice around Alex which along with sales people pushing you in one direction and with every man and his dog from around the world adding the word sani to their products to fool the public means you are in a minefield.
Now, I may not be fully 100% up to date with all the products but the Saniwaste UP is not listed as an offical Saniflo item in the UK so advise you do deal with the manufactures technical departments not a sales company. They dont like the idea of the washing m/c being conected and will argue that the water will be too hot for the macerator but ok for their grey water pumps - Yeah right, nobody washes at 90 or even 60 degrees anymore mister!
My choices would be from the Grundfos that
@CBW linked or the Saniplus (not the Sanibest!) and I would plumb it all in and run for a few months without conecting the wash m/c so you have the warranty should there be a problem and then add the washing m/c via a top connection not a low side connection. Any good service engineer with an ounce of common sense wont bat an eye lid at the washing m/c being connected but might as a warranty claim.