Yap, even reputable managers do not guarantee that you will receive a high fee, but they do guarantee that you will not be hit by a scam, even if the prize received is very small, at least you get paid and do not do useless promotions.
Though it's not that much but having some assurance that you'll be able to get the rewards is much better than being completely scammed by the developers, reputable managers aimed to make sure that every participants will get the amount of shares that they've accumulated but like what you have said the value is still depends from how the project will Push thru.