Focus groups require a lot of careful planning so that they are coherent enough for the results to be interpreted.  

In-depth interviews (IDI) are much more flexible and will allow to gain much more insights. The main drawback is that it will be very difficult to generalize the results of personal responses.

A good rule of thumb is that IDI are useful to identify possible values that trigger the right responses, and that focus groups are more interesting to test these values out on a larger group and develop creative messaging. Focus groups will also be more useful when testing the full creative potential of a campaign.

When the subject is very sensitive, which sexual and gender diversity often is, focus groups can increase the discomfort and participants might be shy to express views that are outside of the norm. In this case, IDIs should be the preferred approach.