Thanee
First Post
I'm not talking about what is written there. The only thing, that can be concluded from the rules text is, that wizards have to use the feat usage granted by the rod, just like their normal feat usage, that is, during preparation. How this exactly works is not exactly detailed. 
Although, 'intent' might not actually be the right word for it, but I don't know any better.
Let's put it into a sentence without using the word 'intent'...
Obviously, when you have to use the rods during preparation, you won't be able to have more than three spells prepared this way (from a single rod) at any time. It's a simple logical conclusion, that there must be some such limit.
Bye
Thanee

Although, 'intent' might not actually be the right word for it, but I don't know any better.

Let's put it into a sentence without using the word 'intent'...
Obviously, when you have to use the rods during preparation, you won't be able to have more than three spells prepared this way (from a single rod) at any time. It's a simple logical conclusion, that there must be some such limit.
Bye
Thanee