Milestone feature is only good for Fiverr and does not add any benefit to freelancer rather make delayed payment.
I feel it’s better to split order in parts and get separate order for individual units of work.
With milestone you only get paid for first milestone when all milestones complete or contract ended.
So if you have made 10 milestone for a very long project you get paid for first milestone when the complete 10 milestone is finished (or project ends).’
Milestone deliveries take 8 days for confirmation, while normal ones take 3 days.
It could be useful in certain cases but overall it’s not what you should choose when your orders can be split in parts and can be placed as separate orders.