No, getting people to sign up is the hardest part!
The value of the claim is what is most important to professional litigation funding firms. You need a decent legal case, but after that, its all about the value of the claim.
Its much harder to get people to sign up for class actions than you might expect, which is why the Australian High Court's recent decision disallowing common fund orders and forcing litigation funders to do book builds was such a blow to the industry. https://www.smh.com.au/business/companies/high-court-delivers-blow-to-booming-class-action-industry-20191204-p53gov.html
Big litigation funding companies typically spend hundreds of thousands of dollars on book builds, which is why Courts initially allowed common fund orders to avoid these costs (which are passed on to claimants as reductions in payouts).
I know this might seem a little counter-intuitive, but the actual Court work is actually the easy bit because over 95% of funded cases settle before trial.