Anybody know anything about the Marantz SD400 cassette deck? 2 speed?

I was just looking at a very interesting vintage (1976) cassette deck that caught my eye.

It is a Marantz SD400 which dates to 1976 and has 2 recording speeds which sounds like it may be a very usefull feature for higher quality recordings.
1 7/8 and 3 3/4.
I have never heard of a 2 speed cassette deck and wondered if the community has or knowledge of this particular animal in general.
I have three Nakamichi decks
Just was very curious as to this particular machine and/or the very principle of 2 speed cassette decks as a new one on me.
Seems like Nakamichi made  a 2 speed cassette deck. Can't remember model number and I think it may have been 1/2 of the normal speed.