I was reading on Wikipedia about the SQ-Ai series adding a "B" setting. This to the body apparently. Did it not exist on previous bodies or is it a lens thing?
The earlier models can do long exposures via the T setting on the lens. the only catch is you have to slide a switch on the lens to end the exposure, so best to block the lens with a cap or cloth to avoid shake before ending the exposure. With the B setting on the SQ-Ai, you can time it all with a cable release to avoid having to touch the lens or camera.
I recently acquired an SQ-A and its become my primary camera. From reading comparisons of the A vs Ai, the complexity of the latter may be a maintenance problem. Its advantage is possible use of metered prism and ease of longer exposures. But I've used the SQ-A with an 80mm lens at f22 in a poorly lit church interior for 8 sec exposure with good results.