Anyone have any details regarding MH's Asean pass?

It says on the website that you must purchase your pass and when ready to fly exchange for tickets. My question is regarding availability to exchange the prepaid vouchers for tickets. Is there a need for availability in a certain fare class or would one be able to get tickets as long as there are seats on the plane?

Also if I was to want to go from Yangon to Singapore would this count as one prepaid voucher or must you use one voucher per leg?

Thanks,
greendx