Does the price difference between a Brompton and a budget folding bicycle represent quality I understand the difference between a cheap and expensive road bike as I have owned one of each. My question relates to an example of two polar-opposite folding bicycles; a budget £129 bike and a £759.99 Brompton. 

Is the £630.99 price difference a result of better components or is the Brompton brand the justification? 

Is there a minimum price that needs to be paid to ensure that a folding bicycle doesn't contain budget components?
Brompton is certainly a well known name in the bike industry. As such, I have faith in their ability to produce a quality folder.

The £129.99 bike uses a design which is sub-optimal for a folder, since a single failure point has the option for the bike to collapse into the folded or partly folded position. Which is not to say it will fail, only that it could, and there does not appear to be a safety.

In addition, the components on the bike appear to be the very basic type whih I would expect to see on a kid's bike, as far as quality. 

Brompton may not have high end parts on this machine, but they appear to be at least ridable quality. 

Whether the difference is worth it, is a personal decision, but I would not consider the £129.99 bike safe to ride for me or mine.