I wish I could say that I did keep on eye on all the "free" scripts out there to see what they are doing; but I'm pretty busy with keeping PhotoPost development going. Besides, most of what I see is knock-offs of features we developed first.
I looked into slideshow transitions a while back and there were some browser issues and load issues for setting up a slideshow (with permissions) on large systems. It's easier to get away with features that "kinda" work in a free gallery since you can just say "well, its free, what do you expect?"; but when you have a responsibility to your paying customers to provide features that work in *their* enviroment sometimes you have to make judgement calls that won't upset your customer base.
You know, there is a Suggestions forum and if your beef is about the slideshow transitions you can make a suggestion and when we can we'll look into it.