Robert Gammon acts dumb as a post again:

Nick says GFX needs a toothbrush for cleaning.

Wrong again. Read much? :-)

... I have a slab foundation and NO basement (plumbing is buried
beneath the slab). The ONLY choice for me is a sewage ejector in the
corner of the garage, near where the main sewer line exits under the
slab with a GFX stack in the corner above the sewage ejector.

Au contraire. That way, you could easily use either heat exchanger,
and you might use the flat spiral version with no pump.

In the 1200sq ft living space I have now, the ONLY unit that will work
is the GFX. There is no room for yours UNLESS it goes in the ATTIC!!!

OK. I give up. You don't even understand "flat spiral."

Nick