Is this a legitimate way to purchase AM shares?
It's one of the many ways.
It's a pass-through, but it can give you direct shares if you want it.
There are lots of other pass-throughs too, here's a guide to some of them:
https://bitcointalk.org/index.php?topic=188550.0Although it doesn't look it if you're new to AM pass-throughs, right at the minute it's probably better to buy the btc-e ones at the current prices. It's currently a little more expensive that BitFunder, whereas it's normally a
lot more expensive than BitFunder.
https://btct.co/security/ASICMINER-PTThis should be a good time to buy. There are big profits coming from sales, and if the APR is suddenly about 50% even for one week, the buzz from that alone should attract some decent money in.