Ask HN: Freelancers, would you pay for a service that let your clients prepay?

Tim, CTO/Co-Founder of matchist here. We're thinking of developing a separate payment product for freelancers. The problem this product would solve is getting your clients to pay on time by having them fund milestones and release payment as milestones are completed (similar to the current matchist payment system). Here's how it would work: 1) When you secure a contract, you set up milestones for the project in the system. 2) Clients prepay for the milestone. There is no fee for them. 3) When you finish the milestone, you ask for payment to be released. 4) The client releases payment. The cost would be $50/month for holding $1k or less in the system. If there was $5k or less being held in escrow, we would charge $100, and $10k would be $200/month. What do you think? Please be honest: Would you pay for this product?