Daunell Zeller Butt​ wasn't up to going riding today so I did a ride with her new trike, a Sun EZ-3 USX HD (http://adulttricyclereview.com/heavy-duty-trieks/sun-ez-3-usx-hd-trike-review/) which we bought from Ajo Bikes (https://www.facebook.com/ajo.bikes.7/) two weeks ago.
After this short ride, I know that I won't be fully satisfied with any trike I purchase that does not have dual wheel drive. While this was a fun ride, and I believe it will improve once I get used to the trike, I noticed that when climbing hills or pedaling with power, which I do a fair amount of when I ride, the trike tries to wander to the left because it's only drive is from the right rear wheel.
While this is minor unless I am on a steep hill, it is annoying. I tried to gauge this by riding with one hand on the handle bars. When I was using my right hand, it was fairly easy to keep the front wheel from pulling to the left; just apply a little pressure to keep the hand from being pulled forward and it tracked well. When I used just my right hand, I had to push with a fair amount of pressure on the handlebars to keep straight and the front wheel still pulled to the left.
When I test rode the Hase Kettwiesel this week and sprinted with it, there was no pull to one side or the other. That was sweet! Still, this was a fun ride and I believe with more practice the pull on non-hills will diminish greatly. However, on hills, there is no way around the pull. While at http://cycledifferent.com/ I also test rode a few tadpole trikes including one with a NuVinci hub and a Patterson dual drive crank. The gearing was interesting and would take some time to get used to. However, every tadpole I tried, and I tried several different models, also had issues with the wheels trying to wander. On the tadpoles it would pull to the right or the left depending on where I was on my pedal stroke. I am sure that would clean up with practice, but it shows a propensity to pull. Also, when medium braking the trike would wander a bit from side to side.