30 miles on a Brompton is ok. Wouldn't want to do more than that on mine. Contrary to other posts on here i find the gearing high and so have had it lowered. They do grind along and the gearing is spaced quite far apart so there's none of that fine tweaking to get the exact gear for that "burst" of speed to get out of trouble or going for it up hills. They really don't do hills. Though I did get up a 17% on mine - just. They're also not good in the wet as the small wheels are prone to slipping.
Go for the 6 speed and dual caliper rear brake as the standard rear brake I had on my last model kept coming loose. I dispensed with the rack as it was heavy and I never used it. Instead go for the front clip with takes a variety of bags which are seemingly bottomless and surprisingly have little effect on the handling. I lug huge amounts to and from work with no problem. Also have fitted usual cateye lights as the ones which come with the standard 6 speed are not up to much.
They do handle well and their foldability makes then so versatile. You can always put it on the bus or in a taxi. I need mine for the train. Must say though that if I didn't need to use a train I wouldn't be commuting on it as it's too slow and I get cut up more than on a regular bike as it's problematic to claim an assertive road position when not going as fast as a bigger wheeled/lighter bike.
Also hope you never, ever get a rear puncture as it's a complete nightmare to get the back wheel off and on. Never seen anything like it the first time I had to take it off. Tyres wear faster than a regular bike too.
Overall very versatile, good handling, good luggage capacity, easy to ride, slow, poor hill climbing, slippery tyres in wet but if you need a bike that folds get a Brompton. Oh and lastly I've had hefty repair bills on the 3 I've had as the plastic bits and long cables/mechanisms/hinges seem to wear out quickly. I get 2 years of constant use before they start falling apart.
Good luck.