Grace 704 vs. 707 Tonearm questions.

Someone gave me a Denon DP 6000 table mounted with a
Grace 704 tonearm. I took it into a shop to have it checked out, and a cartridge mounted (I picked up a Grado Blue). At the shop, the tech noted that the 704 is a unipivot arm, and so is designed to use with a conical stylus, whereas the Grado has an ellipical stylus. He mentioned that someone else who has a turntable in his shop with a Grace 707 arm is looking for a unipivot arm, and might be interested in swapping his 707 for my 704.

How critical is using a conical stylus (vs. elliptical) on
the 704?
If I trade the 704 for the 707 straight up (assuming both
are in equal condition), am I getting the better or worse
end of the deal?