Caveat Emptor: This is not a complete product. It requires the 3rd Edition BAR rules (not included) as an integral component. From the Primer itself:
"The Primer should not be read as rules, but rather should be used in conjunction with the BAR Third Edition rules. ... You must first have read the pertinent sections of the BAR rules for the Primer to help you."
If you don't already own the 3rd Edition rules, Clash of Arms/Wargame Vault will charge you another $6 over and above the $18 cost of the Primer to download them. The rules omission and extra charge should be clearly stated before completion of the Primer download.