@otuuakaa
I know where you're coming from. I've had a few projects that seemed to being developed well and I paid as it went along only to have the critical end steps be something the developer couldn't do (which made the entire development worthless). So I get it.
But again if you're working with smaller developers especially on a project that may take months, then it's usually not going to work to have them not actually get any money until the very end. Most cannot survive waiting that long. Also, in some of those cases I've seen the developer end up neglecting your project to complete others where they know they will be paid that week. Since yours is "guaranteed" anyway they can put yours off to finish ones to get money they need immediately.
Lastly escrow and bank guarantees often times can be delayed by the originator claiming they didn't get exactly what was expected. Or work wasn't done -- even if it was. That occurs often times in mediums like freelancer.
So the risks fall on both sides. This is why shorter term payments with SPECIFIC MILESTONES is critical in my experience. That way you get quantifiable work completed before each payment is made. And the programmer has specific work to focus on with a needed payout upon completion.
This is my own experience and how it's best worked for me on larger developments.
Side note: A quick modification on something here in Boonex the usual process has always been full prepayment. But I've only been fine with that when using reputable developers such as Modzzz or AQB Soft.
Good luck...