You may be surprised to know that both membranes are installed pretty much the same way. The subtle differences depend only on the manufacturer. You can mechanically fasten (mixture of screwing and heat welding) the membranes over the top of a rigid sub-surface such as ISO board or Densdeck. (For the love of all things holy, NEVER directly screw to wood – speaking from personal, traumatizing experience).
You can also fully adhere (glue) over the same surfaces. Fully adhering also allows you to install over structural or lightweight concrete, tectum deck, or any other surface that you cannot mechanically attach to. When you fully adhere the product, you generally get a smoother surface. This looks tighter and a bit crisper than simply screwing it down. So if aesthetics are important to you, then that’s the way to go.
That being said, a fully adhered system is always going to be more expensive than mechanically attaching because the adhesives used are pretty pricey. You can also mechanically attach either membrane utilizing a special induction plate. This plate can be welded to the bottom of the membrane with special induction welding equipment. This is a great way to install when doing a membrane system as part of a metal roof retrofit. It is also ideal in areas that are susceptible to high winds.
Contractors should also be properly licensed to do the job. A good question to ask the company you’re working with is if they will pull a permit with the proper public authorities. If they are not or cannot pull the proper permit, do not hire them. I mean it, you should ask for a copy of the permit pulled.
Here is a helpful article on picking a contractor.