It depends what you are looking for, most of mine are not keen on any chaff, I have tried plenty, so it is not much use to carry a supplement but is useful if I need to give a bit more in the bowl for some reason, a few I have had were also not keen on speedi beet in quantity if trying to give a bit more of a feed, so I use soaked grassnuts as a carrier for supplements in a small quantity and as the main feed for anything requiring a proper feed, they all like it so it keeps feeding more simple and I dont have loads of bins in the feed room.
I've got two good-doer cobs; and they have one feed a day (just to fill up their greedy guts basically so they hopefully don't gob-out on the grass).
They have a handful each (not very scientific, sorry! i.e ONE single handful not a double one) of Speedibeet, coupled with one handful of Dengie Mollasses Free. I soak it overnight.
Just as an aside: DO be careful if changing feeds, back in the horrid winter I thought to change and started feeding them the Dengie Meadow Chop with Herbs. Bad idea! They both went AS-ballistic on the stuff! Easy to be wise after the event, but I looked up the content of it and it was way too high on energy and sugar! So beware, always check first before feeding!
I use both, Rose gets speedi beet to bulk out her feed and I moisten Fatty's zero chop chaff with a bit of water from the soaked speedi beet as it makes him cough if it's left too dry.