If I have to work with fixed prices I prefer misltones. I split the job in 3-4 parts. So, I make sure I get paid for each part and I am not starting on new milstone untill they approve, also, I put water marks on my work, after they approve the milsotnes I sent the files. It works for me, I am 3d rendering specialsit.
Also, before starting any job(especially with fixed price) I look at the client feedbacks form other freelancers.
I think misltones will help you to secure your money better. Rather than you did all work and cleint didnt pay. I would never start work on the next milstone untill previous is fully paid off.