If space is at a premium at home, you might be tempted to opt for an exercise bike designed to fold up and roll away. These will always mean some big compromises in terms of performance, most notably rider position and limited tension settings.
In order to keep the overall footprint low, a typical foldaway exercise bike will use an ‘X’ frame, not unlike an ironing board. In order to keep this dual triangle relatively strong it will need to keep it as vertical as possible, meaning that you're likely to be sitting very upright.
There are some recumbent foldaway exercise bikes available, but the overall size, even when folded, and weight will be bigger.
The other obvious disadvantage of foldaway exercise bikes, is that in order to keep the machine as portable as possible, they will naturally have a lightweight build quality, which will limit tension settings. Plastic will take the place of metal, reducing durability, and the magnetic resistance function, that most operate with, will use a much smaller flywheel to reduce the unit weight as much as possible, significantly reducing its ability to apply resistance as it will be smaller and therefore limit the amount of energy required to turn them.
Clearly they have their place for people with limited space and looking for a low impact cardio workout at home, but if you’re in any way an experienced cyclist, or even an avid spin bike user at the gym you’re going to be left wanting.