I have a Tern Verge x10 that I bought in 2013 (around the time of the frame snapping problems actually, but it wasn't in the recall batch) and have done a few tours and lots of longer (100-200km) rides and it's pretty great. I live in Kyoto, Japan, which is surrounded by mountains and has a large lake nearby called lake Biwa, which from my house and back is about 200km around. I can handle that on my x10 no problems, and it's certainly better than doing it on my old cross bike, or my shopping bike (which was ass-destroying).
The tours I do tend to be either to take my bike somewhere on the train (carry cover stowed under the seat at all times for this reason) and then go around an island or something, or I'll just ride somewhere quite far, then get the train back to Kyoto. My two biggest tours were from Kyoto to Tokyo (~500km in 3 days) and Kyoto to Fukuoka (~700km in 4 days). The Tokyo trip was on a different bike but I did the Fukuoka trip on the x10 and had absolutely zero problems with ride comfort, speed or handling. The Verge, and some of the other sportier folders are really designed for ride comfort more than compact fold though, and while it does fold OK, and fits on the train, it's a really awkward bike to carry when folded. When it's not folded, it's pretty small and light, so very easy to carry short distances if you can't ride a section for some reason.
I'm 6ft, which while not particularly huge, does mean I have the seat high, giving me a high centre of gravity. This can be annoying on steep gradients (I guess over 15%?), as I end up doing wheelies by accident, since the bike has a short wheelbase and if I have a heavy backback too, it's really easy to do. Despite the wheelie problem, handling most climbs (which are probably 5-10% mostly) is not really too different than doing them on a regular bike, since the x10 has 10 gears, with a fairly wide ratio between highest and lowest. The only other small issue I've had was when riding at night, and that's because the wheels are small. Since I wasn't using a bright enough headlamp, there were a couple of occasions where I hit a large pothole, which is bad enough normally, but at night and with 20" wheels it really sucks. I have a much brighter headlamp now so that I can see the road surface properly.
Japan is a fairly densely populated country, so even if you go into the countryside, there will be small towns and villages you can often find somewhere to stay at, and along the south coast there are major cities ever 40-80km, so I usually pack fairly light, with maybe a couple of changes of clothes, tools and a tube, some water and snacks (again, I can just buy stuff at convenience stores or vending machines if I really need). I have nothing attached to the bike, because everything I need fits in a large backpack. I've never toured in any larger countries with longer distances between population centers, but I would definitely have to rethink my load if I was trying to tour somewhere like the US or Australia
I joined this forum to comment in the "Helix Update?" thread, and assuming they don't hit snags in manufacturing, my next bike will be a Helix, which is also a folder, but one that promises comfort without sacrificing fold quality or having tiny wheels. It will replace my x10 and I'm looking forward to trying longer rides and touring on it.