Around 3 months ago I bought a Tern Eclipse 18i folding bike. In fact, my partner and I each bought one. It's a great bike and I don't regret the decision at all. Folding bikes are great for portability, ride like a non-folding bike, and overall aren't much different. However, while there aren't many differences, there are a few, and I'm not sure if it's because it's a folding bike or just because like any bike, there are a few things I'd change to make it better.
First, the headlight in my bike is somewhat defective. Partner's bike light works as expected and blasts a bright beam on the road ahead. Mine is a diffuse beam roughly everywhere ahead. I've tried to fix it to no avail. It seems the led bulb sits too low to properly be reflected to create the focused beam of light. I need to bring it back and have it replaced. Even as a diffuse beam of light, the light does its job and provides both illumination ahead and lets other drivers know I exist at night.
Second, the seat is great for short rides, but not comfortable for any ride of distance, or just longevity. There is no channel down the middle, and the seat appears to be made of highly flexible plastic. This results in going numb after about 20 minutes on the saddle, and of course the painful tingles when off it. I'm going to upgrade the seat to my favorite Terry Liberator model.
Third, the seat post slides down over time. No matter how tight I make the clamp, the seat lowers itself in just riding around. On the one hand it shows how stiff the bike is, which is great for getting power down and pedaling efficiency. On the other hand, I can't stay in optimal position for long so I have to adjust it about every 30 minutes. My plan is to simple replace the seat post with the Biologic pump post. I'm not sure if this will sit tighter, but at least it's more functional. Plan b is to drill a hole at my optimal height and just use a pin to hold it in place. It may rattle and make some noise, but it won't move.
Fourth is to replace the pedals. The short, skinny pedals are great for folding and being unobtrusive. However, for long rides, they don't provide enough foot support, which ends up causing cramps and odd stresses on parts of the ankle. Installing some nice platform pedals should solve this problem.
Fifth, I need to rethink the charging situation. The Biologic re-echarge powers the lights just fine. It's a vampire tap to get the battery pack charged as well. And then, I need yet another set of wires to charge a phone or something via USB cables. I also need to figure out a mounting kit to hold the phone to the handlebars, but to still be able to fold up the bike. The current solutions mount a big case to the bars, which make it impossible to fold the bike all the way.
Six, I need a pannier solution. My Jandd commuter panniers are too big to properly mount on the rack. They do mount, and do work fine so long as I don't hit a big bump or jostle them too much. They sit on the side of the rack with gravity only, nothing strapping them to the rack as on a larger bike. It seems the Tern side bags are always out of stock.
Overall, the bike is fantastic. I ride it daily and have ridden it for many hours on weekend rides. I highly recommend a Tern to any and all. They're great bikes with very few compromises, despite the above desires to modify the bike.