I mixed 2 Maurten320 in liter bottles for a race this year. It works but you can’t just mix them, throw them on the bike, and go. You have to let them sit for a few hours and then give them a solid shake. Otherwise the sodium alginate nodules will just sit on the bottom of the bottle like a sludge. One of those bottles lasts me a couple hours. I carried that bottle plus two gel flasks with 400kcal of 2:1 dextrose:fructose & a caffeinated Maurten100 gel. That would last me ~5 hours…so I mixed up several ‘sets’ of bottles/flasks & every five hours I’d roll in and re-up.
I’ve never tried it in just a 750ml bottle.