Not liking a course would not be a sufficient reason. However, if you found out after joining the course that it was not what you thought it was, and that it was not suited to your needs, you could make a case that leaving the course was the reasonable course of action.
You need to be very careful though. If the dole believe that you have left the course unreasonably, they could stop your payment for 9 weeks, or if they believed that this was an indication that you were not genuinely seeking work, they could stop your payment completely.
If its only a short course, the best bet is probably to stick it out. Otherwise, you would be best chatting to your FAS adviser and obtain their agreement before you drop out.
From a BTEA point of view, participation in the course should not affect your eligibility provided that you are on a social welfare payment immediately prior to starting the BTEA course.
Of course, if you have had your dole stopped because of dropping out, you would not be on a social welfare payment. But otherwise, you can add periods on social welfare payments over the past 5 years to make up the 3 month requirement provided that no longer than 52 weeks separates the different social welfare claims.