OP: For multimode commuting, a Brompton or clone ("brompnot") is fabulous; folds small, drivetrain between folds ("trifold") so less likely to get oil on clothes, but I recommend chain cleaning and melt wax lube from day one. Downside is wheels are small (349 size) so to get sufficient high gear you need an internal gear hub, which adds weight and maintenance cost if ridden in rain, much less so if kept dry. Brompton will (and copies have) made 20" (406) trifolds, they are a bit bigger. 349 trifold will EASILY fit in airline checked luggage, and many have brought onboard as carryon, they make both bags and backpacks to hold them folded. These are all "frequent folders", fold FAST and EASY. Small wheels and skinny tires can ride rough, often not frame space for cushier tires.

20" bifold like Dahon or Zizzo, don't fold nearly as small, if I fly I'll need to put in two separate checked bags. Cumbersome to carry more than 50 feet. Though they can be rolled, but up stairs, gotta lug it. But when unfolded, it matches configuration of Bike Friday tour bikes and can tour like one; Mine is heavily racked and panniered, it is my townie. It is an "occasional folder" for trips in car or by train, easy. But not by air.

Sounds like you might want a 349 trifold brompnot, which used to be a good deal but $300 shipping from asia. But now they are carried on amazon about same price but free shipping. But make certain the features are the same; Usually they are chrome-moly frame and welded, that is fine (brompton uses brazing); But make sure it folds the same, meaning encloses the drivetrain, good speed range, and handebar and seat height correct for you. Check reviews for the model.