It's a bike I love and loathe in equal measures. Hilarious downhill or in heavy traffic (very nippy handling), will drop almost everything away from teh lights. Awful uphill or into a headwind. Flexier than a flexy thing, and for the price, some of the bespoke parts (brakes, shifter etc) are awful.
However they're by far the best FOLDING bike, even if they're not the best folding BIKE.
I bought mine secondhand and it came with M-bars which at 5'10" were way too high, and truly, horribly flexy. At a weedy 10 stone, if I pumped down on them, I could spring the (awful) grips an inch further apart. An S-type stem a flat bar out of the bits box, and a pair of lockons solved that.
Gears - mines a 3. Low is pointless, mid is OK for blasting away from the lights, but spins out too quick. Top is way too high, other than DH. I'd go 2 speed - I believe the sprockets are a standard shimano spline, so you can mix and match your own gearing. The 6 speed is a 3 speed hub (narrower gear spread than the normal 3) with the 2spd derailleur bolted on the end.
Tyre wise I'm running Kojaks I think - silly light skinny things. They work pretty well - have had a couple of flats, but no more than i'd expect from any other tyre.
Mine also has Eezy wheels (great - highly recommended), the firm elastomer (stops it feeling like an early 90s full sus) and spds, cuz the stock brommy pedals are awful if you're used to proper flats.