Reminder: the rest of us don't have the book open to what you're working on. Page references are good.
Easy way to handle a beetle bucker: when will you actually need the thing's stats on its own?
Create it as a buckler, and in its bootstraps, have it bootstrap the Deflect Arrows feat to the hero, adding a bootstrap condition that the buckler is equipped (look at the tags and fields of a normal buckler as you equip and un-equip it and you'll find something to test with).
it should be:
note that the statement I've given you will not work in an eval script or a pre-req, so don't try to copy it. That syntax is only for condition statements.
Hard way:
Take what you've got there, and add the following script (timing can be early, go wth UserFirst, 100):
if (hero.hasminion[rBeetBuck] = 0) then
perform assign[Helper.Helper]
endif
What that'll do is to assign the buckler the Helper.Helper tag unless there is a Beetle Buckler minion attached to the hero. While that tag is present, the buckler won't be visible in the list of shields you can buy. So, once you've added the minion, you can add the shield (I'm not sure if there's a way to have the minion directly bootstrap the shield - the only way I can think of is too clunky to use). Just make sure that the item's price is on either the minion or the shield, not both.