I prefer the 505 also for all the reasons mentioned. Depending on the size of the quilt, I might pin it a few times. I then usually sew my SID going both directions to secure the whole thing. I flip it several times and if I see any wrinkles...I just lift the offending part and smooth it with my hands.
I always wash after using the spray...especially if it is for a baby. You just never know! :D