the fusable batts are ok to use- some adhere better than others- usually you only have a problem if there's alot of starch or other chemical in the fabrics- if the fabrics have been pre=washed the fusable works best-
the stiffness goes away- as soon as the finished quilt is washed.
sometimes it is difficult to fuse the batt to large quilts- easier to use with smaller (twin or smaller) projects- not to say you can't use it for larger projects- it's just more difficult to get the sandwich together.
i like them better than spray---i hate using sprays that get all over-and stink
at least with the fusables no air born chemicals---
i have a couple times had to thread baste around the edges- but other than that i've not had any problems with them working as they should