Just to clear up the confusion:
A pattern cutting bit has a bearing on the top.
A flush cutting bit has a bearing on the bottom.
In most cases, there is no difference in the cutters themselves. Of course, there are "laminate trimmers", usually designed for use in small routers, that may have less durable cutters.
You can use a cutter of any length, just make sure it's cutting in the right place. Ideally, you don't want an extra-long bit to end up cutting your template!