One of the interesting points made is that a group of independents doesn't necessarily need a manifesto. Just a statement about what they think needs to work better and a commitment to work together as a group.
There's an acknowledgement later in the book that outside of local politics this is more difficult because voters need standard commitments to certain behaviour (disavowal of racism for example) and even while manifestos are not binding where politicians use them there are a prime source of information for voters.