BSO stands for Bicycle Shaped Object. Or department store bike.
Bicycle people are not down on them for being cheap. They are down on them for low value. Even at $100 it is not a good value.
Characteristics of a BSO is not just cheap parts but non standard parts. When they do break (which won't be long) it will be hard to replace the part. Some times they do not even honor standards. It might have a non-standard bottom bracket or head set.
Also safety. BSO is just not as strong. If it fails you can get hurt. You have lot more leverage on a folding with long seat tube and handle bars to the frame. It takes more stress than a full size bike.
Start with a bike that has standard parts and standard sizing of components. It can be the cheapest Shimano, SRAM ... groups. If components are not stamped with a known manufacturer then no.
In bikes there a value point where the cost of ownership optimized. As you spend more initially the cost of maintenance goes down. Then you get to a point the components are for weight / speed and more expensive parts and the cost of maintenance goes up.
In a regular bike where is that max value is debatable but some where around $600 - $800 retail. For me max value is to find a bike that was $1200 new and pick it up used for $400.
I don't know as much about folding but that sweet spot will likely be more.
Folding same thing look for standard components.
Without a triangle folding bikes have more flex. Then on top of that hinged parts have flex.
Internal gear hubs are more common for clearance.
How compact is a factor. The more it folds the more opportunities for weak points. Speed of folding. With some assemble required it is typically a stronger set up for the same price range.
Some fold side to side and some fold front to back. Fold back has less side to side flex but it is also more in the more expensive.
Get on the bike and see how it fits. Flex it and look for play. If you can notice play in any of the hinges just flexing with your hand then no.
Bromptom is one of major manufacturers and they start at $1200. I am sure there are some good value bikes less than that - just a data point.
That said if you want a folding BSO go to Wallmart for $200 and see how long it lasts.
On storage hang from the ceiling frees up floor space
Another option is S & S couple. It is an add on the full frame lets the triangle be disassemble. If has all the pluses of a full size bike and the coupling is nearly as strong with no flex. They assemble in like 30 minutes and tools are required. You also need to be able to tune the bike as take apart and put it back together can mess with the tuning. This is more for a person that wants to put a bike on a plane. They are higher end expensive bikes. Not what you are looking for but I thought it was worth mentioning. vaya travel
Another option is a single speed mountain bike. Preferable with a rigid ford. Shocks are really bad on inexpensive bikes and wear out quickly. Because of the sloping top tube it is more narrow. Pull the seat tube, tires, and handle bar and spin the fork 180 so the camber is towards the frame. Single speed as easier disassembly and less cables. Can just loosen the handle bars and spin them or go all the way and remove the fork. A full size single speed mtn is going to out perform even a high end folding bike. More comfortable and reliable.
That is high end bike I picked up $900. It was not stolen - he had the original paper work.