To be honest it's surprising what you can run with perfectly reasonably.
They were a fairly new thing when I first ran with my little 'uns about 9 years ago. We had very little spare cash, so just got a Mothercare returned 3 wheeler. It wasn't designed specifically for running, dodn't have things like suspension, brakes or quick release wheels. It was pretty heavy, and only had 12 inch wheels. However, it was perfectly fine to run with, and I quite often ran up to 10 miles found our pretty hilly country lanes. It was a bit of effort up the hills, but that was to do with the extra weight of the child mostly, rather than the design of the buggy IMO.
I'm sure a properly designed running buggy such as babyjogger would have some advantages, but as I said, even just a bog standard three wheeler (so long as it has a fixed front wheel) is perfectly possible.
The one thing I would say to check out is the height of the handlebar (is that the right term?). I found it really easy to push, far easier than my wife. It was too high for her. Not only did this mean that she found general pushing less comfortable, but she found it difficult to press down to lift the front wheel to turn, I found it dead easy. Some may be adjustable, but I'd definitely try one out in reality, before parting with any cash. A smaller shop may be an advantage here - our local baby shop allowed me to go out on proper runs with several of them to try them out. In fact he even wanted to lend me one over the weekend so I could check it out properly!
