The learning curve when switching from VB6 to B4A is very simple. Android has a different way of handling some things, but you are pretty well insulated from them, and the remaining ones (such as lifecycle) is well documented in tutorials here in the forum.
I've tried both Java and B4A, and B4A is far simpler to get started with (even though I have an extensive background in both VB6 and C#). Much like VB, there is little bureacracy, it just gets the job done.