What is the "Plain" backing?

These patches don't have any special backside. They just come with a simple fleece backside. They are ideal if you want to sew or pin the patch onto something.

What is the "Hooks" backing?

These patches come with the "Hooks" for a "Hooks&Loops" fastener.
Colloquially known as "Velcro", but "Velcro" is a trademark, so I can't use their name in the description.
Basically: You need the "fluffy" side of it on your bag or clothing to stick those patches on.

Why no "iron-on" backing?

There is currently not a lot of demand for iron-on patches.
Also, when you iron-on your patches, you can't ever remove them again, making them basically one-time use.
High quality patches will last you years and years on bags and clothing, so I recommend taking a couple minutes to sew the patches on (yes, even you can do it. I believe in you ;))
Worst case, look for sheets of "Iron-On Fabric Adhesive", and use that in combination with the plain patches.

What shipping service do you use?

Deutsche Post.
Orders in germany will be shipped via "Bücher/Warensendung" (BüWa), international orders via their "Warenpost International" service.

I have an idea for a design. Can you make it?

It depends. How about a quick E-Mail?

How durable are the patches?

They are quite durable. They are manufactured in germany by a company I personally buy patches from for almost 20 years. Even after years on a backpack my patches look basically as new.
(Although they are still textile and will get damaged if you let them scrape along stone walls all the time, for example)