Curious what you find so 'inefficient' about it? IME (although admittedly, I'm no roadie/racer) small-wheeled folders are only marginally less efficient / comfortable that equiv. tire full-sized bikes on decent asphalt. I have an ~equally priced/tire-width gravel bike and Brompton and when I'm in shape enough to run my 15mile exercise loop at a 15mph moving avg, I can do 14.5mph on the Brompton, or ~3% slower/less efficient. Easiest/best mod being an equivalent drop aero position on my Brompton M bars, which also slows the quick steering and provides different riding positions for comfort. The suspension offsets the harshness of the small wheels so that I'm basically indifferent to riding either bike for exercise rides (i.e., no folding).

Biggest limitations for me are rough road/off-road riding and mountainous terrain (gearing and brakes), but it's worth it (for me) for the small folded/rolling options it has. Course, IMHO and YMMV and all.