Advantages and Disadvantages

Advantages;
Tails, by their very presence, will make the wearer stand out, which can be a advantage in many social situations (looking for a partner or (some) jobs, traffic, etc)Provided a suitable mapping is used they may be able to indicate emotions the wearer finds hard to verbalise (the very existence of professional poets and song-writers implies that this is often found hard).

As a fashion-accessory it implies a desire to communicate, something that isn't found in many other such devices. In fact it could be argued that many -if not most- hinder this, for example by making the wearer harder to approach (as in earbuds) harder to read emotionally (for example sunglasses) or even appear aloof (various more expensive products). Unlike other products aimed at communication (like for example smart-phones) there is no need for the "audience" of the tail to own one as well to benefit from it.

The emphasis on involuntary honesty might well lead to tail-wearers to be perceived as more dependable, which could have social benefits.The tail, after some practice, could be used to balance the user (for example in activities like skating).

The tail might be used for simple tasks, like pushing buttons, when one's hands are full. This kind of utility might include sexual activity. While this might sound far-fetched at first-sight the authors suspect that some people might find the concept of a extra source of stimulation that also doubles as a unambiguous feedback mechanism on the received stimulation (tail-based or more traditional) will appeal to certain target audiences.

The tail might be able to comfort the user, in a way much like crossing one's arms would, either for literal heat or as a way to socially shield one's body. It might also be used to do the same for others, again like a arm.

Disadvantages
Tails, as a new sort of "limb", will likely demand new models of clothes, further diversifying that market in a way that will likely lead to price increases. The same may hold true for furniture, like seats, that may become unsuitable for wearers of tails. Of course this might also be deemed a positive factor by early adaptors to those markets.

In some situations, like rush-hour in public transport, the space taken up by the tail may in itself be a undesirable factor.

involuntary emotional expressions might lead to undesirable side-effects.Examples of this could include workers in public positions who aren't expected to show emotions like impatience or even disgust with customers, patients and the like. In the most extreme case this could break political careers, relationships and other social contracts, where it is traditionally important to "keep up appearances". This could lead to the "showing of tails" becoming a taboo subject, much like the showing of legs, necks, breasts and genitals is in many cultures. It should be noted that the way in which some of those parts of the body can involuntarily display feelings (at least of certain kinds) might have been a part in their public display having become taboo. This could be mitigated to a large degree by new models -and types- of clothing and jewellery.

A device like this, especially initially, would come with a hefty price-tag, putting it out of range of large sections of the population. This factor, combined with the above-mentioned possible advantages in employment of tail-wearers could theoretically lead to a more class-based society.

The implantation of technological devices, especially ones attached to the (central) nervous system would come with potentially serious health-risks. Extraordinary care would need to be taken to avoid problems like infection, disabilities and indeed serious communication issues should the device be unsuccessfully implanted or malfunction.