There are many folding bikes on the market, and they all offer something different. But stay focused on what your needs are. The following is what I believe are the most important criteria for a commuting folding bike.
1) The speed it takes to fold and unfold
2) The size after folding
3) The engineering (will the bike stay folded)
4) The ride
5) The weight
6) The price
Once you know what you are doing the Brompton can be folded in less than 10 seconds.
The size is 22 x 23 x 11. Do keep in mind a few inches more determines if you get into the building or not! I can pick up my Brompton with one hand and shake it and nothing will fall out.(try this with any other folding bike). The chain is in the center of the bike after folding to avoid grease stains. The ride is good, althought not like a racing bike type of ride like a Bike Friday or a mountain bike type of ride like the Birdy, but much like a Schwinn or a regular city bike. The weight is around 21 to 27 lbs, an average weight for a folding bike. The price is not the cheapest but definitely not the most expensive like the top of the line Moulton that is about $20,000.
In terms of light weight, Brompton offers the titanium models that can save you 2.5 lbs and offers a softer ride but it will cost you about $800 more.
If you do some recreational riding outside of the city, I would recommend the 6 speed model, as it really offers you a better range of gears for rolling hills, windy conditions, and hills in general. It is now very expensive to do the upgrade from M3L to M6L because they now use different hubs.
As for durability, most of my customers keep a Brompton for 8 to 10+ years. It is very difficult to find a used Brompton. Brompton offers a two year warranty on all the non-wearable parts and five year warranty on the frame.
Finally, a standard Brompton will fit a rider from 4’7” to 6 ft with inseam no more than 32 inches, if you are taller than 6 ft or have inseam greater than 32 inches, an extended post or telescopic is recommended (anyone over 6ft should consider H-Type).
Weight limit: 245 lbs