Hmmm... unfortunately, the only reason I want a tooth there is for chewing. The missing tooth is far enough back that you don't notice it's missing.

In the link you provided I see:

"The design of the new flexible plastic framework takes the danger out of an accidental swallowing of the appliance. In the event that someone did swallow one, it is unlikely that any damage could be done to the lining of the digestive system."

So it sounds like maybe the swallowing hazard has become less of an issue.

It also says:

"Dentists used to build Nesbits for their patients all the time. They were composed of a single denture tooth (usually a back tooth) between two cast metal clasps which attached onto the teeth on either side of the missing one."

I would have thought it was intended for chewing if it's typically used on a back tooth, but then I've never even heard of one until today.

Given the root canals on the two neighboring teeth, it sounds like the best bet is to leave a hole there - right?