Fun fact for all of you talking about how you're going to max this or that, 3 vendettas or 3 land raiders for your allies or whatever.
Go to page 109 and count the choices per slot for an allied detachment.
I'll give you a moment to dry your tears.
Unfortunately what you see is true. Only one choice for every slot, except troops, in which you can take two choices. So if you wanted to take one land raider or one vendetta for allies, go for it. Fortunately for players who like to play games that aren't broken, allies won't let you spam all the UBER JAWESOME units in another codex.