One angle not seen by many. When i bought 5 shares in february 13, they cost me 0.1412btc.  When i cashed out in expiry date june 13, i received 0.17724647;   0.17724647/0.1412=1.2549050076.   --- Besides the daily interest, my gain in BTC was 25.5%. My cashouts from those 5 shares were 0.1176  averaged 83% of initial investment measured in BTC.  Add  0.17724647+0.1176= 0.29484647;  measured in BTC my 120 day gain was 108.8% just considering the interest paid on capital, adding the arbitrage gain... turning 0.1412 into 0.2948 ain't scrubby at all.

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This just to illustrate that since the company insists on tallying everything in USD, there are opportunities to arbitrage against them as it happened in the aforementioned case, using BTC as reference...

All of that, measured in today's  quote of 586usd/btc= $172.75usd. which is only 72% gain ... But i barely ever use dollars so i do not see this as a minus consideration since i fully expect BTC to thrive in the following 2 years.