If you had the required 5k vis your in VMC, SI minima is over 1000agl, do a visual circuit. By day if vis was less than 5k but above 2.4k maintain track and the MDA to the circling area and circle. By night below 5k vis would require a missed approach unless the circling MDA is maintained. Thats the law side.
A reason larger aircraft operators will not visually circle off a straight in approach is usually the aircraft is in the final configuration prior to the MDA. Having landing flap and gear selected is far from ideal to manuevre at low altitude. In most cases the minimum risk solution is to do the missed approach and reconfigure for circling on the next try.
A few questions that need to be answered prior to this event are;
-Are you familiar with obstacles in the circling area
-Will the weather permit safe visual circling
-Will the aircraft require configuration changes and how will this affect your ability to concentrate on flight path and obstacles.
-Are you mentally prepared to circle in the conditions
If any of these are hazy or un-answered than do the missed approach and re-assess your plan of action.