Duragrouch

Completely different animals. The Brompton is the most compact folder, so primo for daily multi-mode commutes, but has the disadvantage of small tires 16"/349 bead diameter; steering more "twitchy/responsive", ride inherently worse, and especially with typical skinny Brompton tires, and I don't know if fatter tires will fit. Most bikes with larger wheels are a much larger fold, such as ones with 20" wheels that are "bifold", whereas the Bromption is "trifold", plus folds with the chain to the inside so less likely to get you or other things oily. However the Helix has a very clever fold that is more compact than bifolds, even though it has 24" wheels. They were able to do this with a swinging rear triangle like the Brompton, but also an innovative folding fork. For longer rides and especially pannier touring, the Helix should be a much better performer, due to two steps larger size tires, but you should check if it still fits within checked bag size of 62" girth if flying. While technically too large, people have brought disguised Bromptons as carry-on luggage. Also, the Brompton, due to the very small wheels, requires an Internal Gear Hub (IGH) for an overdrive to have a high enough top gear. The Helix does not require this so maintenance is much simpler and less expensive, and service in the field on a tour much easier or any bike shop can fix, whereas the number of bike shops in the USA that actually repair IGHs is very limited, one in my town (one of the best).