I wasn't in the actual Exhibition, but I was playing friendlies with it on the stream with Ally/Nairo/Shadow, and Ally and me both think it's not that great (didn't ask Shadow/Nairo). It makes matches come down to who makes the first mistake usually loses, and sets go by TOO fast. Not to mention ICs and MK appear to be absolutely ridiculous with the whole 1 mess up can = match lost.
Personally I don't like it because the sets go by far too fast. I can't imagine a new player enjoying going into their first tourney set and losing 0-3. That's literally only 3 stocks this new player got to play in winners, as opposed to at least 6 stocks normally. I know the idea is to make sets go as fast as normal competitive fighters, but Smash already is ridiculously different, there's no reason to go down from 3 stocks to 1 stocks now.
So in short, 1 stock is fun and interesting, but I don't think it's a good idea competitively.