I have an old Griswald
that takes both 8mm and 16mm. It was my Dad's when he was in the
army in the 1950's. Still works today.
Here is a Mansfield that has the viewer and splicer combined.
You'll see that you still need to pull the film from the viewer in order to
cut the film - but no need to un-spool and reload every time. Not really
any different than if you have a viewer and splicer separate like this:
This is my 16mm setup that I also used for 8mm: #5 is the viewer with
no rewinds, #7 is the splicer. With this set up all I need to do is pull
an 8mm viewer and splicer off the shelf and I'm ready to go.
But if you're more comfortable with a combined unit you can't get much
better than that Mansfield.