You don't need an Ipaf to hire and use booms and scissor lifts.
I would thoroughly recommend getting your Ipaf however, if you've never worked with these machines before, they can be quite daunting. The course teaches you about the safety aspect if the machines and you have a practical test so you can gain confidence using them.
Lots of different machines out there, I normally go to the yard and have a play before it gets on site.