Denise, I do use the spi when solo. But there are a few howevers.
And I assume you mean the symetrical and not the assymetrical, as there is nothing to it to use the assy.
1) With my previous boats I had no problem, and would do it under most sea/wind conditions.They were smaller boats, and in the last boat I had a spi sock I bought from the old sailnet that was made by ATN.
2) I sailed those boats so much, that I could tell right away what they were about to do.
3) The speeds on those boats, also allowed more time to correct screwups and were also more gentile.
4) on my present boat, the situation is different. The
spinnaker is 1500 sq Feet, so its slightly big, and the efforts it does are big too.
So I have only used it solo, I mean, Fred was with me, but he just steers, and I did all the rope/hoisting work. Its a fun thing when its up, but a PITA to get it there. You do need help getting it going.
Also everything happens faster now, and a lack of attention means a broach, so I don't risk it. This year when cruising I used it only once.
Edit: Thanks SD...